The main area seen in those two shots is supposed to be a deep, narrow chasm, so basically it's just one big rectangular brush (with a bit of a tilt to the walls), and then that doorway is just another rectangle carved into one side. Everything else, all the uneven structure of the rock and arched formations, the columns, all that, it's all static meshes. It was kind of funny, the way I just kept dumping loads of them in and slapping them together without really caring what was intersecting what and where, as long as it looked good. A lot of those meshes are 90% in null space at really funny angles and whatnot. Turned out not to be problematic at all, runs fine, looks good. Most of them don't cast shadows so I've gotten a lot of detail in already.
Now if I could just get my damn emitter to work. Figured out how to make a custom door type (rotted little wooden trap door that rotates on a Y axis) just through experimenting, yet I sat there and copied all the settings from a company emitter effect into my own, with slight variations, and the damn thing still shows up weird in-game.