Well, thankfully I have plenty of iron to work with for this on the map.
I am gonna try and avoid altering the cave as much as possible.
Oh, for those a bit curious as to what can show up in caves, here are some of the more interesting caves I noticed in a text file the game gave me after exporting an image, and the source for this fun idea.
Cave 1Opiutesh, "Covercrevice", a cave
1 dragon
1 giant jaguar
19 troglodytes
26 naked mole dogs
18 ratmen
18 antmen
3 giant cave spiders
376 bats
Cave 2Siminrushan, "Entrancecavern", a cave
1 cyclops
23 naked mole dogs
16 giant rats
25 antmen
1 gremlin
7 giant cave spiders
463 cave spiders
312 bats
Cave 3Becors rek Idgagugosh, "Temptedechoes the Subordinate Hollow", a cave
3 giants
19 giant cave swallows
4 giant cave spiders
24 ratmen
27 giant moles
13 giant bats
273 bats
265 cave spiders
I do have to say, depending on what and where things in a cave show up things could become quite interesting. None of these are from the world I am currently playing in, just a teaser of how challenging addapting a cave to a fort could be.
I had no idea that could be done. This should prove very helpful.
It's weird, I had the idea for a pressure plate regulated reservoir just after reading the OP but before reading the first suggestion. Strange I didn't think of it before, it's a problem I had been wondering about for awhile.