[Perdition]

Similar to how the Nameless Shrine has some "hidden" housing locations, I think it'd be cool if, in the Cells sewers, there were 2, maybe 4 spots for player housing. Could make for some interesting RP spots.

[Autumn]

I do thinks this is a good idea

[Shujin]

Tunnelfish rule!

[WaifuApple]

Down this unused path could be a good candidate, and would probably fit just fine with a tweak to make the ladders something you could walk down, with the pot out of the way. I was considering making a small map for it as a proof of concept to submit to this thread, but I couldn't find the floor tiles or the edge wall tiles here, so I don't really have more to offer there.

[Snake]

TUNNEL FISH R-R-R-R-R-RHULE!