Intentionally breached the cave system via a shaft dug off to the side of my fort, then dropped in a kitten and puppy to explore. So far haven't encountered any GCS, forgotten beasts, demons, or elderich abominations. Did run into some trogladites, so I might set up some cage traps to catch targets for my military.
Speaking of military, I drafted all the migrants with military skills plus a few with no skills, gave them iron (no flux) armor and bronze (embarked with extra) weapons. They're doing individual drills now. I'm not sure how to get them to spar, not sure if Toady has fixed the bug, nor am I sure if I have to order them to equip the training spears I made. Doesn't matter for now, I'd like them to get some experience under their beards before letting them jab each other. I'm hoping I won't regret not using axes, I figured spears would be more effective against the blobs that everyone's so terrified of, and I've heard they kill clean.
I'm digging out a tower cap farm right under my brook. During the winter when the brook freezes up I plan to pierce the brook with stairs, then install floor hatches and link to a lever. The end result should be flooding the whole room. Learning from my last fort, I'll make sure to put the lever one floor above the brook so I can stop the flooding if I need to. Should be interesting.