Being in Adventurer mode, the other day, and finding a Dwarven stairwell pit with a lone (ramp-slit accessible) room at the bottom with no other apparent exits out of it[1][2] (though, later, I encountered ampersands wandering around the place, so the game, at least, thought that there was some sort of connection with something down there, even if it was only fudging it) I went around "L"ooking around intently to see if there was actually some sort of hidden hatch or door in the bottom room... Now, if there were hidden doors/etc, they would of course be placed as part of a procedural-furnishing of the (currently just procedurally-dug) dwarven halls, but I could see that being a feature.
Probably also has cross-over coding needs with getting traps and trap-interactions remedied so that Adventure Mode doesn't have (by default, by the relevant init settings) trap-ignore status.
[1] I found a second settlement with a whole column of ramp-rooms, maybe a dozen Z-levels of them, but ultimately the bottom one had zero non-upward exits (visible), and the others were up/down between themselves, only. That settlement also seemed to have attracted ampersands. So far, none of my other explorations (with another adventurer, the original one succumbing to a whole-body skin disease caught from the sprayed-on extract from a ridiculously easy-to-kill ampersand or two) have touched upon dwarven settlements, but human and darker-being settlements (of varying current ownership and intermediate provenance) seem to be quite normal, and once I worked out the trick with Megabeast caves, I found the all-pervasive subterranean systems interesting (though haven't yet tried to navigate between cave-sites using them).
[2] Had considered trying to embark on/near it to either discover its layout through play or by getting the Reveal thing to show me anything I'd missed.