Some ideas about the area the clan lives in!

The clan is situated in the Hellwell Undercroft, so the majority of daily activity happens underground.
(an undercroft is 'the crypt of a church' so lets run with that theme!)
SO its an underground city! Probably a lot of overhead space with no small amount of columns to hold the roof up! Being naturally formed (and having a ton of spiral dergs digging through the rock) there is likely to be a lot of smaller crevices, nooks, niches, etc.




Sweet! we have a general setting! Now how about the buildings? Well, being a mixed clan with different needs and wants, the buildings/dwellings are probably equally diverse! I can imagine the majority of buildings being quite colorful and decorated because, well, the surroundings are quite dingy and any dragon needs something to lighten up the space! (Lamps. so many fun lamps. Some post style, some on wire crisscrossing streets and stuff. Bro the city GLOWS.)
Speaking of space, being underground, there is most likely a limited supply of land to build on. So what do you do where you can't build out? You build up! (shhhh OSHA and building codes don't exist here) Because of the size of the clan, I can imagine there being tunnels to larger storage rooms / the barracks / hibernation nooks / etc. underneath the city.





Again, because of the size of the clan, there are probably smaller districts that are starting to form. Now we can start to imagine the more specific setting of the city. For example, maybe the city started when the clan (in its younger years) first settled against the back of a larger semicircle type deal, like the deepest part of a C. Now, as it is getting older and expanding, the city has started to fill out more and more of the 'C'. Maybe now, there is a larger gate at the entrance to welcome travelers, merchants, etc. The gate is both a wealth flex and a form of security.

Regarding the plague-y side of things, the city is perpetually warm and damp. Because of this climate, there are quite a few things growing on the walls, floors, and roofs. Mushrooms be absolutely THRIVING here. Yes, the cave does have its own weather patterns, but it doesn't super help the humidity and heat. Imagine if you can, Japan in the summer. But without the light. Hot, humid, and rainy. And also dark. Yikes. At least the city has colorful buildings and lanterns though, right?
There are a few pools of plague soup in quarantined spots around city. Occasionally this will displace some dragons while the site is cleaned up. Luckily, there is a lot of temporary housing set up across the city.