Building a surface fort, with most of the housing being in rows of Roman-style
insulae, with workshops on the first floor, and bedrooms on the second(each workshop+2 beds are in a single unit). Each insula provides 20 beds and 10 workshops. Initially tried to build from stone, except I couldn't put out enough blocks. Tried to use wood for interior walls and floors, but almost ran out of wood. It's closing on the second year, and now my stone industry is capable of providing enough stone(plus enough labor) to get a new insula built within about a season - if only the carpenters could put out beds, doors, and cabinets so fast.
Currently have 4 built insulae, one on the way, and almost 160 dwarves(extra free housing is provided in the manager's office). The military is almost fully steeled, with a few people preferring to use goblinite scrap, and some wearing one boot for some reason. The steel industry is pumping out bars like mad, as is the stone blocks, and I just got ash-based products up and running. All from abuse of the manager system. For steel, I have each step of the process(smelt hematite->make pig iron->make steel) require the previous step be done(smelt hematite triggers after the previous steel). Definitely an improvement over older versions.
I think it was a titan. Titans can be based on all sorts of creatures, not just those present in the game.
Titans are literally Forgotten Beasts that happen to live on the surface.