This is the art for the kuo-toa settlement in the Stygian City. A small, underground river flows past the 13th level, which is how the fish people found the abandoned settlement and moved in. On the 15th level, a broken bridge across the pit separates the kuo-toa from the myconid colony below.
By the way, I’ve revised the plans a bit for the rest of the project. Here’s what I’ve got in mind now:
1-2: The village
3: Villagers’ mines
4: A maze of tunnels and collapsed chambers overrun by mold
5: Caverns inhabited by giant bats
6: Catacombs
7: Goblin village
8: Giant spiders, huge webs strung across the pit
9: Ancient temple
10: Industrial workshops
11: Hag’s thralls
12: Night Hag’s palace
13: Kuo-toa settlement and river
14: Main kuo-toa settlement
15: Bridge across pit between kuo-toa and myconids
16: Myconid colony around a crumbling fountain
17: Ancient oracle and library with a long-abandoned scholars’ camp containing notes about the pit’s history
18: Undead/Demons. Magic Stuff?
19: Ancient prison
20: Ceremonial jumping point with temple
21: The bottom: Ghanya (with several variants of the bottom level, including a sealed vault/prison, underdark entrance, trash and debris and aboleth lair).
1-16 are pretty much locked in, but if you’ve got any thoughts about what might fit in anywhere below that, let me know. If I like it and I can work it in, I just might.