After 5 years and ~106000 created wealth (with zero imported, so long as our starting equipment doesn't actually count), The fortress of Ironhalls has received it's first forgotten beast, Akung, a towering humanoid composed of green glass with wings, it undulates rhythmically (for some reason this makes me think of them as some sort of dancing, prancing beast who kills you while singing a merry tune...), Beware his poisonous gas. No casualties, I actually (miraculously) managed to get everyone, even the animals, inside before walling off the main stairwell. I then realized the point from which i'd been dropping stone walls on the fish-men was also an access point for the beast, and sealed it off. It nearly got in anyway as the pump stack, directly connected to the stairwell for dwarf power, was not sealed off at the time. It was on floor 12, vulnerable, idiot dwarves and useless junk, when my stoneworker, Stony, finally reached the site and sealed it in, the wall was just on the other side of a pump. I don't know if it's actually a building destroyer without dwarves to path to as it has shown no interest whatsoever in any of the many constructions in the cavern or the pumps, but I'll call it a close call anyways.
Luckily, 2 years earlier, I had dug out the tree farm and flooded it (ever so slightly on the full side), leaving me a place to plant crops, although there aren't yet many trees and all the seeds but what's left in the mature plants (around 135 right now) are down there. Having a 50z tall fort has it's down sides, especially when I've never used an alert before(and didn't this time either) and it took a while to get everyone inside.