When it comes to making maps for organic spaces, my main trick is to use the solid noise rendering function in GIMP, apply a black/white threshold transformation to it, and smooth out the resulting spaces as desired. I got the idea from this video about making cave maps.
As mentioned in the previous part, I like the idea of a multi-level dungeon with levels both above and below the main entrance, so I figured I'd start out with a 12x12 grid for the main level, 10x10 for the second (in either direction), and finally an 8x8 for the third (in either direction). I turned on turbulence in the solid noise dialogue box for the ground and upper levels since that tends to result in more narrow spaces, while I left it off for the lower levels to get more open caverns underground. I may switch to a hex grid in the end since that tends to work better for irregular spacing, but I'm using a square grid for now since I can snap to that in GIMP for places where I want some fortifications within the mound or just general ease of copy/pasting between layers.
I also played around some with viewing multiple layers simultaneously, to make sure that I could get some connections between more than one at a time.
After that, I started working on smoothing out the spaces, starting with the main level. About 40-50 keyed spaces sounded good for the overall dungeon, so I aimed for roughly 14 on the main level, 9 on each second level, and 4 on each third level. This was also a good time to think about Jacquaying, so I looked for opportunities to have loops and partitions within each of the middle three levels to go along with multi-level vertical connections.
Fully keying out the dungeon will wait for later, but as something to keep in mind, I also read about termites on wikipedia, which produced some interesting nuggets about their nests:
Termite nests tend to have choke points where a single soldier (or a small number, at worst) can make a stand to hold off invaders.
The termite queen and king reside in a highly-defensible "queen cell".
Some termites have fungal gardens within their nests.
I had been planning to have some choke points between areas already, so that first point encouraged me to make them even tighter and more frequent than I might've done otherwise. The tidbit about the queen cell linked up perfectly with my thought of the hanging moss having invaded from below; the queen cell would likely be in the underground portion of the nest to keep it as far from invaders as possible, and the hanging moss came in through an area that the termites had thought was secure (possibly an underground water reservoir). And of course, I just had to have a fungal garden now, likely in an isolated area where it wouldn't get in the way of normal traffic.
At this point, my backstory for the dungeon is that it was originally a settlement of some kind, then giant termites attacked it and turned it into a nest. Thus, there will be some walls and even a few stairs left over, but mostly just on the main level; the upper and lower levels are largely spaces that the termites carved or built for themselves. The "hive caller" is whatever brought the termites in the first place, and since my chimeric faerie is associated with a "stone of protection", I think that'll be the hive caller. I haven't thought about the exact mechanics for how it'll work yet, but it's some type of magical stone that's in the possession of the termite queen, who in turn has been possessed by the hanging moss.
Are there still free termites in the mound? If so, are they trying to fight both sets of invaders or just the sundew/faerie? Can these termites actually communicate with a PC party, or will they seem to be simple animals? These are all questions for the future, but it's good to identify them ahead of time for idle brainstorming.
Meanwhile, here are the current maps, with a first pass at room numbering and showing level connections:
The symbols and numbering are pretty crude for now since I just drew all of it manually to save time. On a more useful note, I marked in secret doors for areas where I want the structure of the nest to be thin enough to break through without needing specialized tools. The areas behind them are where I can put some treasures unrelated to the termites, or maybe they can be areas that the termites sealed off for various reasons (e.g. the secret entrance at 13 can be an emergency escape route for the queen and king).
Next time, I'll start going through the maps to nailing down what those spaces will actually be, figure out what's in the rooms in broad terms (i.e. empty, monster, treasure, trap/trick, special, or combinations thereof), and work on finer details like minor elevation changes, dungeon dressing, and checking that there's a sense of logic to the layout (e.g. should the connection between 18 and 19 be sealed?). I'll probably also talk about some of the other things I read on wikipedia about termites, scorpions, and narwhals and how I can use them in the monster designs as well as what other monster types I might have in the nest.