## Monday, September 23, 2019

### Cave Dice

When I first started running my annual Outdoor Spoliation games, the intent was to explore the Original D&D Wilderness adventuring rules as closely as possible. In that ruleset, most of the action is driven by random outdoors encounters, where each type of monster comes with a "% in Lair" as one of their primary statistics (still visible as late as 1E AD&D). So you generate a random monster and then find out if it's holed up in a cave lair of some sort, with actual treasure.

But how to handle those randomly-determined cave lairs that might pop up anywhere, any time? As usual, I really prefer mechanics without some complicated table that I need to go paper-shuffling while players wait for me to adjudicate when it comes up. In this case I came up with a dead-simple method using a single d6, based on the shape of pips on each face. It's served me well ever since, in many different circumstances, and is IMO impossible to forget:

 Random d6-based cave generation

In my application, I assume the the 4 and 6 cave results have no other exits, likely where the monsters are settled with their treasure. Therefore the 1, 4, and 6 results are all terminal; 2 and 3 lead to one other area; and only the 5 has any branching (namely, 3 other tunnels for PCs to explore). If this branch shows up, then depending on a whim I may split the monsters up into two groups and plan to pincer the PCs when hostilities commence.

Of course, many tunnel complexes will be a straight line; on the other hand, the 5 branches may lead to more branches, which may continue bifurcating indefinitely. That said, the average number of areas per complex is (oh god, here I go).... letting x = expected areas down any one tunnel:

And this result was double-checked by Monte Carlo simulation in C++.

#### 25 comments:

1. Interesting idea. Do you have a starter area with more than one exit (start the cave complex with a '5' type setup)? Otherwise, there's (I believe) a 50% chance that the 'dungeon' ends on the first roll. Or perhaps, the first few rolls use a 2D6 and select the 'best' roll?

1. Could do that, personally I don't; I'm okay with the area being just a single immediate cave (on "4" or "6"). In practice I don't let it start with a "1" (reroll).

2. Dan you have the best tricks

1. Ha! Thank you so much! :-D

3. Fantastic. Really. I love this a lot.

4. Really good, simple, practical stuff - much better than continuing to reuse the same half dozen or so generic "small cave" maps over and over and over, like I've been doing for the past few decades...

1. Right. Once in a while I turn around and go, "I need more fully-fleshed out caves" and use a random generator, but then keeping track of shuffling the paper and losing where they are, at the table I keep coming back to this every time.

5. I really like this, thanks! No reason why it can't apply to man-made dungeons too, definitely going to try this out.

1. Thank you for saying that! I hadn't considered using it for engineered dungeons, maybe I should try that myself. :-)

2. I might! Do you roll these on the fly? I'm intrigued by mapless dungeon crawling (or map-as-we-go) but not sure if I could pull it off.

3. Right, I do roll these during play. For the OD&D lair situation it's manageable because going in I know there's exactly one batch of monsters inside (or maybe I split them in two, per above). If there was any more complicated stocking than that I'm not sure I could manage it, either.

6. Have you read Veins of the Earth by Patrick Stuart? It's a book for generating massive cave systems within the Underdark (designed for LotFP, but should be pretty compatible with OD&D).

Parts of the cave generator can be a bit... shonky (e.g. you roll 2d6, and the size of the cave is basically determined by how far apart the dice fall), but it's full of ideas and could easily be more formally codified, and it's got exactly this sort of thing. The 2d6 roll determines the size of the largest cave exit, then half that for the next one, and so on until the exits are too small to use.

1. Well, that's kind of interesting. I like the smaller-and-smaller tunnels idea. Admittedly I don't follow the LOTFP stuff very much, and I'm not fond of the "where dice land" mechanics they use in places there (can't really analyze or balance that statistically).

2. I'll admit I didn't much care for the "where the dice land" mechanic either, and it's the first thing I changed. It was interesting though, as it attempts to solve the problem of how to make a major pointcrawl in 3d space.

As for LotFP, Patrick Stuart does some pretty out there modules, and I suppose it makes sense for him to target the same system his publisher uses, but the OSR games are all largely interchangeable. LotFP has a few nice bits, but I don't use it myself.

3. Interesting! I think Paul has run one of the LOTFP modules in the last year, and the content was challenging the boundaries for some of our players.

4. Yes, I can appreciate that. I once played in an actual LotFP game and... well a single Summon spell led to a horrifying end to the campaign. They call it "weird fantasy" for a reason.

The LotFP specific parts in Veins were really just things like hooking onto the d6 skills rules for getting past difficult climbs and getting lost in the dark.

7. What's the difference between a small cave and a dead end? Do the small/large cave have exits of some sort? If not, there doesn't seem to be much functional difference between a small cave and a dead end.

Also, it seems weird to find a four-way intersection in a natural cave system. One would expect mostly binary forks in a natural cave system, with the intersections of two perpendicular tunnels rare.

1. I'm sure you're right on that last part, I'm just being inspired by the shape of the pips.

The idea for the small/large caves is those are both places where the lairing monsters could be found, as opposed to the dead-end. One has a tighter fight space, while the other has more room to spread and maneuver. When I use this they're terminal (no exits), but of course you could expand with something else.

2. Frankly as a first stab I broadly assume the "4" cave is 40x30 feet, and the "6" cave is 60x80 feet, or something like that.

3. I think a dead end could be a cave-in, sheer drop etc? Or bars across a tunnel. In a megadungeon scenario it could be a shaft down to the next level...

4. That's great, too!

8. That is a neat little system! I agree that it is indeed very easy to remember. Having only read it once I am not in doubt that I would be able to use it at my table immediately and without any reference at all.

I could not keep myself from finding the distribution of the number of locations. If anyone is interested it can be seen here (link). I grouped all frequencies of 15+ locations.

Considering the frequency of 1-2 location dungeons I think I might consider making a rule for my own use to either start with an intersection or re-roll all dead ends until 3-5 locations are reached. It was also kind of surprising to see that one dungeon in 10 will contain 15 or more locations.

1. That's great, thanks for sharing that! Indeed, long-tailed distributions will mess with your head. :-)

9. I get why you made 5 the intersection based on the pips, but if I were using the chart I'd swap 4 and 5 so that 1 is a dead end, 2 and 3 are tunnels, 4 is the 4-way, and 5 and 6 are caves just so it's an easier mental grouping - it doesn't break up the caves, and it splits tunnels and caves with the 4-means-4 in between.