New WIP (was working on this all night while my flatmates were out getting drunk):
Ignore the low-res terrain and placeholder materials.
A problem I encountered (apart from the mesh issue below) was that it (because of how I'd textured it) started to look like an old FPS like Hexen or something, will walls and floors made of tiling bricks n blocks. Hopefully I'll be able to get rid of this with some good hi-res grunge overlays, specular control and lighting
I am going to keep working on this, even though I realised that all my modular meshes were just slightly wrong, and as such allow an annoying amount of light leakage... I have to fiddle with my Max settings, but it shouldn't be a problem for my next environment.