The Iris Walls (Patreon)

One of the major zones of the Nimbus underground.  There are dwellings carved into the softer stone, which you can tell from the window-like holes in the wall.  Lighting in the underground is dim so good thing they have excellent night vision!  They have managed to concentrate the bioluminescence of the flora by means of artificial selection to make some means of light (lamps, etc) but, you know, it's still a cave.