I breached the first cavern layer in search of non-stagnant water. One word? Carnage. There's about a dozen corpses visible in the small part I've revealed so far: bat men, drunians, a giant olm, even two trolls. I promptly sealed up the place: it didn't have water anyway.
The second layer was subsequently discovered, and this one had water! I'm currently digging an underground basin to collect it, sealed off by an artifact floodgate I had lying around (I'm sorry, queen Udib, your bedroom is 'horrible' again).
Also, a dwarf didn't get silk cloth for his artifact and went crazy. He eventually died on the doorstep of my temple: Helmdragons has seen its first death. A small burial room/temple for the god of death was designated next to the farms, and the dwarf was buried there without issue.
I've also filled in a new level. The fortress guard and militia squad now have a training room, there's a jail guarded by a hyena the elves sold me, and both mayor and guard captain have received their rooms. Work on the hospital has also been finished, and the built-in well will hopefully be filled soon.
I'm seriously questioning my defenses. While in an emergency I could lock the whole place up and seal off the entrances, if anything actually gets in my eight warrior dwarves are going to have one hell of a tough time killing stuff with their copper equipment. Curse you, metamorphic layers!