Despite being wildly inefficient compared to a player fort, I've always thought the worldgen forts were pretty neat. So I set out to reclaim one, and as it turns out the new features in v50 make them significantly more treacherous than before. The issue is those ubiquitous obsidian clusters of fun.
Recall that the worldgen dwarves use a standard scheme for their fortresses, centered around a hollow ramp spiral that runs vertically from the surface all the way down to the magma. Unless the fort connects to a subterranean highway, they often even had the sense to wall up the holes where the ramp shaft crosses the caverns. Unless the megabeast that ruined the place is still in residence, reclaiming one used to be generally pretty safe. However, as it turns out, the dwarves who built today's site delved the shaft straight through a substantial number of obsidian surprise packages. Unpausing gave me several "what devilry..." and "something evil emerges..." messages, not to mention both water and magma falling down the shaft.
That turned out to be easy to manage though, as the sudden guests went chasing after former inhabitants first , since some of them had spawned in the depths. A few forbidden doors and hasty walls later, they were contained in various corners of the old living quarters. No, the real annoyance is that, as it turns out, the surprises don't trigger when mined, but when *revealed*. Tonight's reclaim effort finally crumbled when a dwarf trying to bury someone's mangled skeleton got deep enough to trigger another six or seven at once, including a couple of clear glass monstrosities.
Looks like next time I take one of these on, I'm going to be meticulously building airlocks every few z-levels. Fun!