Improved Rules for Foraging and Hunting

A while back I wrote about a somewhat more detailed version of the rules for foraging and hunting from the Expert Set. Forget all of that. This is better.

Foraging: When a party is travelling through an area that has a decent amount of plants growing in it that humanoids can eat, there is a 1 in 6 chance that the PCs can collect 1d6 rations of food per day by simply picking up what they spot growing next to the trail they are travelling on. If the party includes characters with special wilderness skills, they have a 2 in 6 chance to find things they can eat.

Hunting: When a party is staying at one campsite for a whole day, they can send out hunters or hunting parties to hunt for food. At the end of the day, each hunting party returns with 1d6 rations of food (1d8 if the party includes a character with special wilderness skills). While the hunters are out hunting, a wandering monsters check is made for each hunting party and for the camp.

Water: Unless otherwise specified by the GM, the party comes across sufficient sources of drinkable water each day they travel through the wilderness. No rations of water have to be consumed at the end of the day. (Assume all characters refilled the water rations they consumed during the day when they had opportunities.) Characters spending most of the day inside dungeons do not have access to sources of water unless the GM specifies otherwise, and must consome a ration of water at the end of the day.

Lack of Food: Characters who do not eat one ration of food in a day, suffer 1 hit point of damage and can not heal damage naturally without magic.

Lack of Water: Characters who do not have one ration of water in a day, suffer 1d4 hit point of damage and can not heal damage naturally without magic. After 3 days + 1 day per CON bonus, the character dies.

The idea here is that in an average wilderness environment, parties will not have much trouble keeping themselves fed by hunting, but replenishing their supply of rations will either take a considerable amount of time or require splitting the hunters up into several smaller groups. Both options mean an increased number of wandering monster encounters before the party makes it back to a town or their base. It’s a very simple mechanic but gives the players a lot of variables they have to pick, like the amount of food supplies they keep, how they pack them among their PCs, hirelings, and pack animals, at what point low supplies might be a reason to turn back, how to split the party, deciding which hirelings to send into the woods to uncertain fates or who to leave behind to guard the camp, and when it might be worth it to keep pushing ahead while starving instead of stopping to hunt. I see a huge potential for amazing unscripted adventures simply because a randomly encountered wyvern made off with the mule carrying half of the party’s food.

Extensive playtesting will be needed to dial in on the best die to roll for the amount of rations provided by hunting so that it severely inconveniences the party without getting it completely stuck and unable to continue towards their destination. But otherwise I’m really excited to give this a test run.

What’s the function of a Stronghold?

Working on my Ruins of the Shattered Empire campaign, I was thinking again about Kenshi, a wonderfully weird sandbox indy game set in a desolate post-apocalyptic wasteland full of bandits, robot skeletons, ancient vaults, ninja, cultists, crashed satellites, insect men, random orbital lasers from the sky, and flesh eating giraffes. The game has no story. You just start somewhere in the desert, with nothing but the shirt on your back – if your character is one of the lucky ones – and your only goal is to survive by getting something to eat and avoid getting eaten yourself. Unless your character is one of the mentioned robot skeletons. It’s a wonderfully odd game that feels like something that would have been made in the early 80s if the technology had existed back then. People who like things like Veins of the Earth or Ultraviolet Grasslands will probably appreciate the style. There are various bare bones NPCs around the game world that ask to join your team or can be permanently hired for a one time payment. The desert is full of hungry beasts and nasty bandits, and while it certainly is possible to play the game as a lone wanderer, a very attractive option that opens up very early on is to build a small base with a wall that protects your people while mining ore to sell in a town or working on a patch of dirt to grow your own food. You still keep getting attacked by raiders who’ll easily break down your gates after a minute or two and loot your little storage shed, and so you can easily find yourself in an endless cycle of expanding your base to provide more food and income to expand your group with additional warriors, so that you can expand even bigger to add your own workshops to make your own weapons and armor instead of having to buy them. It’s often compared to Dwarf Fortress and Rimworld, with it’s own special type of weirdness and hilarity.

In addition to building materials, you also need to first research construction plans for new buildings and equipment, and for that you need books of ancient knowledge. A few of which can occasionally be found in stores for a hefty price, but the more rare ones require you to go explore ancient ruins in increasingly more dangerous parts of the massive wastelands. And setting out on an expedition to find and explore these ruins always reminds me of good old D&D wilderness adventures. The ruins themselves are all pretty small, so I wouldn’t call looting them dungeon crawling, but getting your group of scavengers to those places and hauling back your loot to your far away base is just like wilderness adventures should be.

I’m also now remembering how I always found the use of NPCs as part of PC’s “gear” in Apocalypse World a really cool approach, and how they can be used as really nice adventure hooks, but I don’t want to go onto another tangent and actually get to the point.

Base building in Kenshi is in many ways an economy sim in which you figure out how to assign your characters to different jobs, optimize workflows, manage your resources, and invest your profits into new technologies and expanding your operations. It’s a lot of fun on a computer that takes care of all the math, and you spend hours upon hours on it by yourself. It’s not something that translates to playing a roleplaying game as a group. All the stronghold building rules for RPGs I’ve come across so far fail because of this. But the aspects of defending your stronghold against raiders and having to go out into the dangerous wilderness to gain resources you need to maintain and expand your base are also endlessly exciting, and those activities are the daily bread and butter of D&D adventurers.

I am really intrigued by the idea of giving the players the tools to take over any abandoned or cleared out ruin, fixing it up and fortifying it, and using it as their main base of operations while they are exploring the surrounding wilderness. And after some pondering on the subject, I believe the best way to approach this is not to start with any mechanics for upgrading a base or price lists for various expansions, but first figuring out what kinds of functions the stronghold should play in a game that is still fundamentally about going into dungeons to find treasure. This really is just throwing around some ideas and sorting out my own thoughts on this.

What a Stronghold should be for

Safe Resting Place: This really is the primary function of a stronghold in the wilderness for adventurers. A stronghold provides a place where the party can rest and recover from their ordeals without having to make wandering monster checks. I plan to run the campaign without clerics, so healing either takes a good amount of time to recover naturally, or use up healing potions that are valuable and can not be infinitely replaced. This should make a place where the PCs don’t have to worry about monster attacks.

Treasure Vault: If the players have their stronghold guarded by mercenaries while they are out of adventures, I would consider storing their new treasures in their vault as having “returned with treasure from the wilderness”. Since they are also no longer under constant threat of being attacked, that means they have completed their adventure and can get the XP that their loot is worth.

Supply Depot: In addition to storing treasure at the stronghold, the players can also store supplies of food, water, ammunition, lamp oil, and tools. The stronghold might even have its own well or cistern to provide an endless supply of water. Using their base as a supply depot means that the players don’t have to carry as much supplies to get to the dungeon and back, and if they should be running low while in the dungeon, a resupply trip to their stronghold would be considerably shorter than returning all the way to the nearest town. Of course, they first need to get the supplies from the town to the stronghold, which can be a small side adventure in itself.

Necessity of Hirelings: I love hirelings as a game element, and really want to see wilderness adventures turning into large expeditions of a dozen people or more. Having just four or five PCs as the whole party is nice for a lot of campaigns, but I think wilderness exploration campaigns should be at a much larger scale. Wilderness exploration is more than having one outdoor combat encounter between the town and the dungeon entrance. That’s the kind of game the Expert rules are for. Having a stronghold full of supplies and treasures means the players need someone to guard all of it while they are away. And they probably don’t want to leave some mercenaries they picked up in a tavern alone with all their money for days on end on a regular basis, so they should also have some trusted retainers to leave in charge while they are gone. With a more permanent base, you also probably will want to have additional servant staff to cook and make repairs, tend to the animals, and you can see how this can escalate very quickly.

Money Drain: One thing that lots of people have been thinking about a lot for a very long time is what players should be doing with all the money they make on their adventures. Especially in a campaign where XP are gained from finding treasure to mechanically support the PCs’ endless hunger for more gold, the whole thing becomes increasingly less believable if the characters are already drowning in more gold than they know what to do with. Conan is always up for an opportunity to steal some gold because he’s constantly broke. In such stories, the heroes spend their loot on wenches and ale, but enjoyment of luxuries is not something that you can really get across through the mechanics of a game. Players saying that their characters go on a massive tavern crawl after an adventure is maybe fun once or twice, but stops feeling rewarding after that. A stronghold is a great way to drain the coffers of the PCs. Every expansion or upgrade to their base costs money, and all the guards and staff need to be constantly paid for. The wages are pretty cheap, but if you include proper tracking of time (without a meaningful campaign is impossible, as you know) then all the time that the PCs are spending in the wilderness while searching for ruins, days spend healing from injuries, weeks spend learning new spells and creating potions, and whole months stuck inside waiting for the end of winter, this all adds up.

Merchant Access: This is related to the aspect of Supply Depots above. Once the players have established their stronghold and have to make regular runs to the next town for considerable amounts of supplies (all those hirelings need to eat), they can become important enough customers for traveling merchants to make detours to sell their goods to the PCs. Maybe not with whole wagons, but at least with a handful of mules. In addition to regular supplies, such merchants can have a number of special items for sale that the players might be interested in, like potions or maps, and also provide the players with new rumors when they are away from civilization for long.

Trouble with the Neighbors: Even with solid fortifications and mercenary guards, the treasures and supplies inside a strongholds will attract all kinds of people and creatures. Some might be out to raid the place, while others might simply not appreciate newcomers in their territory. The possibilities for adventures beyond the default treasure hunting are endless, without the typical situation of sending the players to chase after prepared adventures. Pacifying the surroundings is a good way to let the players be proactive and deal with situations in whatever ways they come up with, without giving them a villain with a plan they have to stop before it is too late.

What a Stronghold should not be for

Economy Sim: As I mentioned earlier, managing your resources and working out production systems can be a lot of fun if you’re playing by yourself on a computer, but just isn’t something that works as a roleplaying game. Adding a smithy to your stronghold or constructing a wind powered water pump for your well can be fun and exciting, but I think it really shouldn’t turn into a resource management game.

Generating Income: In Kenshi, I started my first base as a small mining camp to simply mine ore, smelt it into metal plates, and sell them in the next town to make money with which I would buy anything else I need, such as food and medicine. Getting your stronghold self-sufficient and even profitable is a fun idea, but that would go directly against the overall premise of the campaign and one of the main purposes for having a base. The upkeep costs for having the stronghold is meant to provide the financial pressure to keep the PCs going into dungeon to search for more treasure. The strongold being a source of money instead of a giant money sink would work completely opposite to that. While being landowners with servants working for them can be a fun idea for some roleplaying games, it just doesn’t fit here.

Seat of Government: Related to the point above, becoming the biggest dog on a stretch of the frontier and clearing the surrounding land for settlement can be a great motivation for characters. But once you get into that kind of stuff, there’s not going to be much room or time for continuing to go dungeon crawling. You could still go into underground places to fight the enemies of your domain, but then you end up with a completely different type of gameplay from sneaking around in the dark to steal treasure without alerting the inhabitants.

This as a broad overview of where my thought are on this subject at the moment. We’ll see if I’ll get around to put further work into this and develop it into some kind of system with established mechanics and procedures.

Discovering Sites in the Wilderness

I’m a big fan of wilderness sandbox campaigns, but never been really enthusiastic about the hexcrawling approach, in the sense of “go from hex to hex until you find something”. A 6-mile hex is something like 80 km². Even a large castle might not be noticed while simply moving through such an area, and if the area is forest or mountains, you would have to run straight into it. Spending some amount of time to search a hex to see if you discover something also doesn’t seem convincing to me. If you’re a treasure hunter, you wouldn’t just pick a random spot in the wilderness and start searching it with a fine comb. That takes way too long to find anything of interest. What I believe adventurers would do is trying to make their way to sites that they already know about and that look promising for holding treasure.

Under this approach to adventuring, the players first need to have clues where to look for treasure and adventure. So here’s a couple of ways that PCs can learn of new sites to add to their own map.

Highly Visible: Castles and watchtowers are commonly build on high points where they can overlook a lot of the surrounding areas. Sites like that could be spotted by simply being in the same hex they are in. Or in particularly clear terrain, even by being in a hex next to it. Though if the site is hidden among trees or mountains, it would remain hidden even party is moving through the same hex.

Sites on Roads and Rivers: If a site is directly on an old road or a river that the party is using for navigation, the players discover it automatically when they pass that spot. In some cases, it might even make sense to road signs or something similar point the players that something worth investigating lies down a side path from the road the party is currently traveling on.

Found Maps: Players can find maps among the treasures they pick up which show some sites that are known to them, and some sites that are not. This allows them to go search for and discover the new locations by following the clues on the map. They could also buy maps from certain individuals, or be given a map as a reward from grateful NPCs.

Rumors and Quests: Locals simply tell the party about sites they know but are not on most maps. This also provides the players with some vague idea of what they might have to deal with when they get there.

Following Tracks: After a random encounter, if the players try to follow fleeing enemies or follow their trail to where defeated enemies came from, the tracks can lead them to a nearby site where the creatures have their lair. If no matching site is anywhere nearby on the GM’s map, a quick lair can be put together with a small cave or campsite plan and rolling up a lair encounter by the wilderness encounter rules.

By using all five of these methods to give players hints where they can find new sites they didn’t yet know about, it should be quite easy to make it all feel quite natural and a consequence of the players’ actions, rather than the GM deciding the party needs a new site to be send to. It’s not a big red glowing sign telling the players “the next prepared adventure is here”.

Expanded Wilderness Travel Rules

Expanding on my table for wilderness travel rates from a few days ago. For maximum efficiency, I am simply listing travel rates in 6-mile hexes. I think in the same way that a 10-minute Turn is not exactly 60 rounds or 600 seconds, we don’t need to treat a 6-mile hex as exactly ….31680 feet. (I had to look that up, and so would you. Those units are stupid!) In actual play, both duration and distance are abstract fiction that don’t relate to anything physical. And characters in the game world would not have actually have any means to measure either distance or time with any accuracy anyway. In a game, if players ask an NPC for a distance to a place or how long it would take to get there, that NPC would give them a rough guess like “some 10 miles” or “three days, if you keep a good pace”. That’s good enough on the players side. When I run wilderness adventures, I am fully in the camp of “the players never get to see any hex maps”. The hex map is a tool for the GM, just like random encounter tables. And for the purpose of telling the players when they arrive at a point, you really only need hexes. Miles are meaningless from a mechanical point. Or at least they are if you have a system for travel speeds in place that doesn’t have any granularity smaller than a hex. Which is what the following tables are all about.

Land Travel

Encumbrance Easy Terrain
Difficult Terrain
Unencumbered 6 hexes 3 hexes
Encumbered 4 hexes 2 hexes
Heavily Encumbered 2 hexes 1 hex

As I mentioned in my previous post, this is based on the assumption that a healthy adventurer with no significant load can cover 36 miles on a road or easy ground in a day. That would actually be quite impressive for a real human, but still plausible. However, in practice characters traveling through the wilderness to explore dangerous ruins and caves will be carrying quite a lot of stuff, and mostly deal with difficult terrain once they get off the roads, so that travel rate will rarely come up in actual play. So for the sake of easy use by the GM, I have no issue with that table maybe getting a bit high.

River Travel

River Speed
Upriver
Downriver
Base Speed 4 hexes 4 hexes
Slow Flow 3 hexes 5 hexes
Fast Flow 2 hexes 6 hexes
Rapid Flow 1 hex 7 hexes

From all I could find, going at 3 miles per hour ± the speed of the water is a pretty common speed when paddling on a river. Take that by 8 hours and you get 24 miles per day, or 4 hexes. If you go with the water flow, you’re going to get a bit more, if you’re going against it, you’ll get a bit less. If you wanted to, you could probably quite easily calculate what the flow speeds in the table above would be in miles per hour. But since player character’s won’t be measuring that during play, “slow”, “fast” an “rapid” are good enough for me.

Switching Pace

Something that I think would be neat to have is a system in which you can seamlessly have the party switch from one pace to another, like going a certain distance by boat, then continuing by foot on a road for a while, and covering the rest of the day’s travel on a mountain path. It could be done, but for that you really would need 1-mile hexes, and that’s just way too small for my own needs. At this point, I am diverting from my usual approach to get the mechanics all neat and consistent, and instead just guestimate things. If the party wants to move into a hex with terrain and encumbrance that would allow for 2 hexes per day, just check if they still have half of the day left. If yes, their camping spot for the night will be in the next hex. If not, it’s going to be in the last hey that they reached. It’s imprecise, but good enough for me.

Random Encounters

I know many people like to check for random encounters in the wilderness once per hex that party moves through, but I found that to actually not make much sense to me. Yes, you are moving through more area when traveling at a faster speed, so there are more spots you pass through where you could encounter something. But you’re also going to spend less time in each spot, which reduces the chances that you are in any one given place just as other creatures are passing through it. I think that just cancels each other out and travel speed does not actually affect the chance of encountering something on a given day. Only the total time spend in the wilderness does.

So I simply roll for random encounters four times per day. Once in the morning, once around noon, once in the afternoon, and then one more check during the night. Regarding which hex a random encounter takes place in, I am again going with “make something up”. If a party is traveling four hexes in a day and a random encounter happens during noon, is it locate in the second hex or the third hex? I don’t know, pick one. It really doesn’t matter.

To check for an encounter, roll a dice that reflects the likelihood of encountering anything in the area the party is traveling through. Going with my paradigm of something always happens on a 1, smaller dice result in more encounters, and larger dice in fewer encounters.

Encounter Density Encounter Check Dice
Desolate d10
Sparse d8
Average d6
Populated d4

I can totally understand if this system is a bit too abstracted and not granular enough for some people. But I like its neatness in how easy it is for actual use during play, while still overall being somewhat plausible in the distances a party can cover in a day and not diverging too significantly from the distances and durations you’d get with using the exact numbers from the Expert Rules.

Overland Travel Speed

The 6-mile hex has long ago established itself as the default size for overland travel on hex grids for a number of reasons. And I rally quite like it myself. I like consistency.

From Hydra’s Grotto (click for more detail)

Hexes are a nice aid for GMs in that you can break down all distances in easy to track chunks, and more importantly can note down where the party of PCs is currently at by simply marking the hex they are in.

One thing that D&D has always gotten annoyingly wrong however, is that the various systems for overland travel speeds all don’t work with 6-mile steps. This whole thing is getting really rambly, but I don’t know how to get it more concise right now, and I really want to get some new stuff on the site.

In B/X, movement speed outdoors is either 24, 18, 12, or 6 miles, depending on a character’s encumbrance. Great. But if you are traveling through forests, deserts, hills, and broken lands, this speed is reduced to 2/3 the normal progress. So 16, 12, 9, or 4 miles. Only one of these is a multiple of 6. Same issue even now in 5th edition. Movement speeds of 30, 24, and 18 miles work great. But not if you cut them to half in any kind of difficult terrain and you get rates of 15, 12, and 9 miles per day.

You don’t actually get the most convenient feature that using a hex grid can provide. You still have to track how many half hexes or even third hexes the party has moved in a given day.

The most convenient for GMs would be a system in which all possible distances are increments of 6 miles. And the only way in which this really works is using base speeds of 36, 24, and 12 miles per day, with all forms of difficult terrain reducing that by half to 18, 12, and 6 miles per day.

Encumbrance Easy Terrain
Difficult Terrain
Unencumbered 36 miles 18 miles
Encumbered 24 miles 12 miles
Heavily Encumbered 12 miles 6 miles

However, 36 miles is really quite a lot.

But how unrealistic is it really? There are plenty of sources for military references for marching armies that put good progress somewhere in the 24 to 30 miles per day range, though often much less than that. And if you look around for advice on how far people can expect to hike for a day, those 24 to 30 miles numbers show up as well as recommendations for beginners who might be unsure how far they can actually make it in a day. 36 miles in a day is significantly more than that.

But a party of PCs in a wilderness exploration game is usually not an army on the march. Nor are they inexperienced hikers. Also, all those numbers assume 8 hours of moving per day. That leaves 8 hours of resting in camp and 8 more hours of… what exactly? If you’re on vacation and hiking for fun, there’s plenty for you to do during that last third of the day. But moving through dangerous territory to get to an even deadlier dungeon is very much not a vacation. I think adventurers crossing the wilderness would do a bit more walking each day than tourists. And another very important factor is that in most systems, being “unencumbered” usually translates to very light gear with very little weapons, tools, and supplies. When a party is crossing through the wilderness for several days, they won’t be unencumbered. If using the numbers I’ve proposed above, 36 miles in a day would be something that only really happens for messengers in a hurry. No loitering around, carrying only the barest necessities, sticking to roads and easy ground. And in that context, 36 miles in a day does not seem that implausible. Much more common, at least for the campaigns that I run, would be traveling with a medium load, mostly going through forests and swamps, which would reduce the usual distance per day down to 12 miles. A much smaller number.

And at the end of the day, we’re talking about a game that has hit points as one of its basic mechanics. We’re not running an actual simulation of anything here. Also, any amount of miles really is just a made up number in an almost undefined virtual space, not any actual physical distances. Might some people think that 36 miles in a day is a bit of a stretch? Sure, why not. And I am not going to argue with anyone on whether that can actually be sustained for more than a day or two. But having to bother with only full hexes and not dealing with any fractions or partial hexes is a big convenience for running fantastical adventures in a made up space, and that’s the part that really matters.

A proposal for a river navigation mechanic

Most RPGs I’ve seen mention about navigation that when you’re following a road or river, you automatically get to your destination eventually, and you only need to make rolls for navigation if you’re going cross country or across the ocean.

Yeah. Kind of. But not really.

If you’re on a river and your destination is to just go downstream to the coast or a city you know to be further down the river, then there’s really no way you can get lost. But things look completely different when you’re trying to go up a river and you come across forks where you have to pick going left or right.

I’ve been on a couple of canoe tours throughout my life, and I’ve been doing the navigation on most of them. Though I have to say that was on very easy rivers in Germany, on waters that have regular traffic and existing infrastructure and very good maps. And we were going to destinations that had been selected by people who knew that those routes would be very easy to follow even to amateurs. And even then, I’ve had many cases where I really had no clue if that big branch to the right is the already the third big branch to the right we need to take, or if one of the branches we already passed looked much bigger in person than it does on the map. The map has an accurate scale on it, but with no means to monitor your exact speed, that’s still only of limited help. Now imagine that deep in the wilderness, following a map drawn by someone with no access to aerial photography or surveying tools.

In my rivercrawl campaign, going to a site will almost always consist of going upstream all the way to your destination. And since all wilderness travel will be along rivers, going with the “you can’t get lost when you follow a river” approach isn’t going to cut it. (Though conveniently, getting back to base at the end of an adventure will be very easy, and going with the current also a lot faster.) Something else is going to be needed.

Making a complete map of an entire river system spanning hundreds of miles with all its little side arms really isn’t practical. You could theoretically let players give it a shot on a blank hex map with very small hexes, but I think that would be very tedious and not feel like it reflects the kind of maps actual river explorers would be using for their notes.

Instead, I want to go with an entirely skill check based system to navigate through the networks of small side branches that fork of from the main waterways that are depicted on the main overview map. My own GM map only shows branches up to the third order, and I intend to let players find their ways on those without navigation checks. It’s only for the rivers even smaller than that that this system comes into play.

Maps are items that characters can find or sell that have instructions on how to reach certain hidden places from an easily recognizable and unmistakable landmark. Every map has a dificulty based on it’s quality. Using a very good map is an easy task, while using a poor quality is a very hard task. The difficulty is further modified by how far the destination is from the clearly identified reference point on the main rivers. Since I have all my travel times in increments of 10 miles, (1 mile per hour times 10 hours per day), I increase the difficulty of the navigation check by +1 for every 10 miles that you try to follow the map.

If the navigation check is a success, the party reaches the destination in the shortest time possible given the distance and their travel speed. If the check is a failure, they still get to their destination, but for each number that the check fell short of the difficulty, the travel duration is increased to require one additional random encounter check. I do three random encounter checks for each day of travel, plus one check per night. So missing the difficulty by three adds a whole day on the water searching and backpaddling, and you also get another night to rest and potentially have another encounter before you arrive at your destination. Since I usually have random encounters at a chance of 1 in 6 for every check, getting two or three checks added to the journey generally shouldn’t be much of a problem. But for journeys deeper into the smaller rivers, having someone with a good navigation skill and paying for high quality maps can become really appreciated.

The fun part comes with the additional use for navigation checks to make your own maps of the unknown rivers you explore. These maps can be very important if you want to find a place again after having left it, and can be sold to other characters. To make such a map, a character makes a navigation check. The quality of the map and the difficulty to use it depends on the result of the navigation checks. For Worlds Without Number, I’ve decided to make it 20 minus the navigation check result, with the minimum difficulty being 6.

WWN makes skill checks with 2d6, so I think it’s a great idea to let the player roll one of the d6 either open or in secret, and the other d6 gets rolled by the GM. That way the player has a clue for the final quality of the map, but can not be certain how accurate it really is. The ultimate difficulty for using the map remains secret for the GM, at least until the players trying to navigate with the map have reached the destination and will have found out for themselves.

For players going to discover unknown sites by going into these small rivers blindly, one simple approach would be to simply roll a d20, and the result is the number of random encounter checks until the party finds either a small randomly generated site or a larger site whose exact location on the river has remained undefined until a party randomly discovers it. Since you might always need a monster lair or pirate camp if players try to track randomly encountered enemies back to their hideouts, it’s a general good idea to have a couple of those ready at hand anyway. And players can be required to tell the GM that they plan to go on a random exploration a few days before the game.