Mapping caves - exploration trepidation

Make caves scarier to explore.

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Cave systems have been used as dungeons forever. They are have been used countless times in dungeon crawlers (see adventures like Incandescent Grottoes) but also in horror games like Call of Cthulhu. They often lack what I crave in a cave exploration scenario though - the creeping fear of being trapped.

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Mapping

Caves are hard to map in the real world. They are very 3D and a different beast to overland mapping or structural schematics.

Let go of the idea of a concrete map. We’re going to use a pointcrawl method with some extras. I’ve talked about pointcrawl dungeons before, check that out here.

Let’s look at my map.

Image Credit: me

The vertical axis is depth in this case, so A is nearest the surface and I is the deepest.

Ovals: These are caverns. They function like normal dungeon rooms, and are big enough that space isn’t of concern unless I write otherwise.

Lines: These are the connecting tunnels. The number of side by side lines on a connection represents how many people can walk side by side. Dashed lines are extra narrow and present a risk of getting suck (see below).

Markers: The perpendicular dashes are markers for travel time. It takes a dungeon turn (10 minutes) to travel between each of these.

Let’s run through an example tunnel, the one from A to F. The tunnel appears wide enough for 3 people at A, a turn later it becomes very narrow, then a turn after it widens to be comfortable for single file before arriving at F. This would take 3 turns (assuming no delays).

Note how players can think they are going down a wide path but it ends up quickly shrinking down. This is caving horror.

Squeezing

If players pass through a dashed passage, they need to make a check to avoid getting stuck. Keep this simple, something like a dexterity check is good here.

If they fail, they get stuck for a dungeon turn. Here’s the cruel bit. They keep making checks until they succeed to get free.

Give them disadvantage or a bane of some kind if they are carrying/wearing a lot of gear (plate armour, a heavy spacesuit).

~watch your players shit themselves as they roll encounter checks while one of them is stuck in a letterbox shaped opening~

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Climbing

You can require that in steep sections of passages that characters climb. The angles of the passages are drawn on the diagram, use your judgement of whether the angle is steep enough for climbing to be required. Use any set of climbing rules you like.

When a climbing check is required is up to you. You might raise or lower the difficulty based on other factors, like a pre-laid route or a character carrying a lot of gear. You decide what failure looks like, it could be damaged gear or a fall - where you use fall damage in whatever system you are using.

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Restricted space

You can make rulings as needed about how the restricted space affects what players can do, but I have two rules I keep in mind:

• In dashed paths, characters can’t swap order. In single lines, each must squeeze (as above) past each other to do so.

• In single or dashed paths, attacks except those made with polearms or compact weapons are at a disadvantage (weapons hit walls, shots are very hard to line up).

Monsters might be exempt from these rules if they’re adapted to the space.

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Wrap up

Take this unpleasant scenario and fill it with traps, hazards, and opponents. Next week we’ll discuss two ways to make this even more of a nightmare.

Oh, and if you are looking for a nice notebook to draw your cave maps in, check out my hexbooks, notebooks designed specifically for GMs running hexcrawls and mapping dungeons.

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Recommendations

Sale: DriveThruRPG has a ‘cosmic horror’ sale on right now. My biggest recommendation is Death in Space. It’s an ‘everything is falling apart’ semi-post-apocalyptic cosmic horror pseudo-hard-sci stew with a lean and clean ruleset to back it up. Also, the book is beautiful.

Book: Colm Norrish released a fantastic (and free) Into the Odd adventure, Mountain Underground. I’m impressed by how it mimics the art and layout style of the Into the Odd Remastered book, well worth grabbing if you play Into the Odd!