I'd try to use support posts at all the points where tunnels meet. Too many holes there and you have a nice format of supports already, just copy/paste some into your joints and you'll improve a lot. I'd also suggest detailing the above ground area a little more so that the brushes just don't run together. .. mainly where the access ramps are, the hole just appears and looks to 'cut' and 'neat'. Otherwise, great concept and with some VIS help it will get even better.
you have to climb right to the top of the ladder until you stop, then jump. there was no other way of doing it tho. that ladder has to be fixed to the track support, and i cant cut a piece out for a platform, so it had to go behind the ladder.
also, the ladder is the only way up from the bottom. once you fall down there, people can camp and wait for you. so im gonna move the terrain up by the caves in that area, so you can go into the caves from there, then there'll be 3 ways out of the bottom of the main room.
another problem i noticed is you can see thru the ceiling in the main room. its made from inverted terrain, with a textured brush above it to stop the light getting thru the gaps, but it still does in some places
ill fix all these bugs tomorrow, and then ill start a full compile. theres brushes between alot of the meshes, so that should help FPS