Rules for Caving

This post is basically "Veins of the Earth climbing rules, but this time for crawling!" I've always felt like the one thing Veins lacks is rules for fitting through small spaces; it makes reference to crawling and hands and knees and squeezing on your belly, but there's no actual rules for them. So, I decided to write my own; they are, naturally, pretty much untested.

I should say—I'm assuming you've read Veins of the Earth by Patrick Stuart and Scrap Princess, and have it handy for quick reference. If you haven't, go read it, it's great. 

CAVING RULES 
I broadly divide caves and passages into three categories. (The zeroth category are regular passages that are tall and wide enough to walk through, but those don't really count.) They are:

1. Crawl or Chimney. These are passages that are about 2-3 feet at their narrowest. If they're horizontal (so that's a tunnel 2-3 feet high), you have to get down on your hands and knees and crawl. If they're vertical (so that's a shaft 2-3 feet wide), you have to press your back against one wall and your legs against the other, and then "walk" up or down the wall. This category also might include war mines, air vents, laundry chutes, and things along those lines.
2. Squeeze. These are passages that are about 1-2 feet at their narrowest. If they're horizontal (a tunnel 1-2 feet high), you have to lie on your belly or back and slither forward like a worm. If they're vertical (a shaft 1-2 feet wide), you have to brace your arms and legs against the walls and shuffle upwards or downwards. This category might also include hollow tree trunks, kobold or goblin rat-holes, and crawling under beds.
3. Choke. These are spaces that are less than 1 foot at their narrowest, but can still be traversed (some chokes simply aren't, they're just too narrow). Chokes are most commonly just one section of a crawl or squeeze, but they sometimes go on for several feet, and sometimes even longer. Chokes might also include storm drains, slot windows, and the gullets of large monsters.

The generic verb used to traverse these kinds of passages—and super deep caves in general, really—is "caving." When you check a skill here, it's your caving skill.  By default, these rules assume nobody is particularly trained in caving. 

Facing, Turning, Vision, and Caving Order

Generally speaking, you cave forward head-first, and once you're in a tunnel, you can't turn around. At a crawl, you can see behind you (or under/above you, if it's a chimney), but in a squeeze or choke, there's just no way to get a clear view. This means that once you get going, the order at which you're all moving forward—who goes first, second, third, etc.—matters, particularly for combat. Decide your caving order before you enter, and then stick to it. 

Rules for moving past party members (and other stuff) is covered later on. It's very difficult, but theoretically possible.

Deciding to travel feet-first can occasionally be helpful. If you're descending downwards, for example, it's usually easier; the flipside is that you lose much of your vision. If you go feet-first through a squeeze or choke, you can't see past your own body, and thus count as caving in total darkness (see caving check modifiers later on).

Caving Checks, Size, and Speed

When you cave, you make an X-in-6 caving skill check; the X there is determined by the speed at which you're trying to go. Caving very slowly is more likely succeed, caving very quickly provokes all kinds of failures. (For these rules, I'm assuming a default speed of 30 feet per 6-second round.)

Speed per Round	Crawl	Squeeze	Choke
5 ft.	[7]-in-6	[4]-in-6	[3]-in-6
10 ft.	[6]-in-6	[3]-in-6	[2]-in-6
15 ft.	[5]-in-6	[2]-in-6	[1]-in-6
20 ft.	[4]-in-6	[1]-in-6	[0]-in-6
25 ft.	[3]-in-6	[0]-in-6	[-1]-in-6
30 ft.	[2]-in-6	[-1]-in-6	[-2]-in-6

A 6-in-6 or higher is an automatic success; a 0-in-6 or lower is an automatic failure. Thus, an ordinary person physically can't go through a choke at 20 ft. per round, just as they could go 10 ft. per round at a crawl and suffer no issues. 

You should be caving checks every ten minutes or every time the passage changes significantly in size or shape, whichever comes first. 

Just for scale, 5 ft. per round is just over half a mile per hour, and 30 ft. per round is just shy of 3.5 miles per hour. A very slow crawl and quite a brisk walk, respectively. 

Caving Check Modifiers
When caving, there are conditions that can affect your chances of success, separate from your raw speed. 

For each of the following that are true, your chances of success are reduced by 1-in-6:

• You are wearing heavy armor or carrying an ordinary shield
• You have something in one of your hands, like a sword or torch (this can count twice if both hands are occupied)
• You have a pack on your back. You can still bring gear on caving runs, but you either need to push/pull your pack separately, or else have so little gear that it doesn't significantly add to your body mass.
• You are in total darkness (or otherwise can't see, like when you travel feet-first through a squeeze or choke)
• You are in some kind of other unfortunate condition, like underwater or pushing aside rubble (this can stack from multiple effects)
• You are an exceptionally large person: someone very fat, someone very tall and muscular, or a large species, like lizardfolk or half-giants

But, for each of the following that are true, your chances of success are increasing by 1-in-6:

• You have a rope-line through this passage or fixed handholds, like pitons or carved notches
• You are being helped by another character, one who is doing nothing but help you (they can't be actively moving or fighting while they help you)
• You are trained in caving (if you're like, a god-tier master expert caver, this might worth +2, not just +1)
• You are a small species or otherwise small person: gnomes, halflings, goblins, kobolds, etc. (Whether or not dwarves get this bonus varies by table; my inclination is to say no, since dwarves are typically broad and not known for being nimble, but that interpretation varies.)

Again, if your odds reach 6-in-6, it's a guaranteed success; if your odds reaching 0-in-6 or lower, it's a guaranteed failure.

Some examples:

• You are crawling at 10 ft. per round (6-in-6) while wearing plate (-1) and a rucksack (-1), but are being helped by a friend (+1): you have a 5-in-6 chance of success.
• You are squeezing at 15. ft per round (2-in-6) while underwater (-1) with no lamp (-1), but have a rope to hang onto (+1): you have a 1-in-6 chance of success.
• You are a kobold (+1) going through a choke at 5 ft. per round (3-in-6) while using handholds (+1), and have been living in caves (and thus caving) your whole life (+1): you have a 6-in-6 chance of success.
• You are Fezzik (-1) squeezing at 5 ft. per round (4-in-6) while pushing aside rubble (-1), with no lamp (-1) and a full pack (-1): you have a 0-in-6 chance of success.

Failing the Caving Check

Just like Veins, when you fail the skill check, you roll a single d20 and compare it to each of your stats, trying to roll under them. If you fail the CON check, you suffer all consequences—otherwise, if you pass, it's just the lowest result on the chart that you failed.

Crawl

Constitution	All further fails are cumulative.
Strength	Your muscles shudder and strain. For 1d6 rounds, your pace slows by 5 ft.; this might bring you to a stop.
Dexterity	Your limbs cramp up. You stop in place for 1d20 seconds.
Intelligence	You lose your confidence. Next caving roll, you count as trying to go 5 ft. faster than you currently are.
Wisdom	You smack your head on the ceiling, and suffer 1d6 damage.
Charisma	You panic and cry out; someone else has to roll, too.

Squeeze

Constitution	All further fails are cumulative.
Strength	You stick your arms and shoulders somewhere they shouldn’t go. Save vs. vice-clamps or become stuck.
Dexterity	Your legs and hips get caught on something behind you. Save vs. contortion or become stuck.
Intelligence	Your gear scrapes against the floor, walls, and ceiling. You lose 1d4 randomly-determined items.
Wisdom	Claustrophobia sets in. You freeze in place until someone calms you down.
Charisma	You panic and start flailing; save vs. panic or become stuck.

Choke

Constitution	All further fails are cumulative.
Strength	Stuck, and you can’t expand your chest. Save vs. crushing force or start suffocating.
Dexterity	Stuck, and you can’t move anything at all. Save vs. crushing force or be paralyzed until freed.
Intelligence	Stuck, and panic overwhelms your mind. Until freed, you can’t speak other than gibberish or understand anything more than simple instructions.
Wisdom	Stuck, and you start to hyperventilate. You’ll pass out in 1d6 rounds.
Charisma	Stuck, and you start screaming. All NPCs make an immediate morale check; monsters will be attracted by the sound.

Getting Stuck
When you are stuck, you can't move. You can maybe wave your arms a bit and maybe kick your legs, depending on how and where you got stuck, but that's about it. You can't move forward or backward, you can't turn or twist or anything, you can't reach your belt or pack, and you definitely can't swing a sword.

Most cavers that get stuck get stuck near their hips or shoulders: they go forward, they stop, and then they cannot go backwards. It's very not fun.

Getting Unstuck
Once stuck, there's no one single way to get unstuck; players should get creative in their problem-solving. That said, there's one important guideline you should follow: a stuck character cannot free themselves without something changing. They need tools, or friends, or a shift in the caves; they can't just make another Strength roll or something and unstick themselves. Their own faculties alone won't work—that's why they're stuck in the first place.

Here are some possible means to get someone unstuck:

• Break their bones so they can bend through small spaces
• Grease or slicken the passageway to make it slipperier
• Chip away at the rocks wedging them in place
• Carve away at the flesh that's keeping them trapped there

Of course, if someone gets stuck, you don't have to free them immediately: someone stuck makes a great barrier against pursuing monsters. Plus, once they're dead and their flesh has rotted away, their bones, clothes, and loot will slide out easy. 

Passing by Comrades, Corpses, and Other Obstacles
If you want to try to make it past an obstacle, like the corpse of a monster or a fellow comrade, treat the passage as one size smaller. A crawl becomes a squeeze, and a squeeze becomes a choke. If it's smaller than a choke, you've got to clear the obstacle out before you can get through.

If you're moving past another (living) PC, they also have to roll a caving check based on the speed you're moving past them. If one of you gets stuck, you both get stuck.

Vertical Passages and Climbing
These rules assume that the passages you're travelling through are relatively flat. This is, of course, rarely the case in actual caves, and so it may happen that you'll end up caving vertically. If you're caving and starting ascending or descending at any angle stepper than about 40 degrees, you count as climbing a slope (Veins 213). If it's a vertical or almost-vertical shaft, you count as climbing a hard climb (Veins 214). When this happens, you should make two separate skill checks, one for caving and one for climbing. Follow the caving rules found here and the climbing rules found in Veins.

If you fail one of those checks, roll the d20 as normal. If you fail both, roll a single d20 and use the results from both tables. This if you fail, you're suffering two different consequences.

If a result says that you should fall and get stuck, either:

• As soon as you are unstuck, you fall; OR
• You fall, and then get stuck where you land.

Whichever makes more sense in-context.

Descending Headfirst
Most cavers travel headfirst, so they can see where they're going. This is normally helpful, until the cave starts descending downwards. At this point, a caver is relying almost entirely on upper body strength with their body weight press downwards, trying to crawl lower, into the dark.

If you fail a climbing check while descending downwards, use the consequences from two tables higher than the elevation angle you're travelling at. Thus, if you're descending a slope headfirst, you use the consequences from the Very Hard table, and if you're descending a vertical shaft headfirst, you use the consequences from the Human Limit table. Falling headfirst down a dark shaft is very bad news indeed.

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I've boiled this down onto a handy cheat-sheet you can download here: Caving Quick Reference.

I also highly recommend you watch a couple of extreme caving videos, and read this New Yorker article about the deepest cavers.

Let me know if you get a chance to use these rules; they're mostly unplaytested, so I'm curious.