The only thing I could think of, if you needed or preferred sticking with segments, is a simple retexture of the
sci-fi corridor you mentioned - seems to be the closest segment to what you're looking for, and (not speaking from actual knowledge or experience), try opening up the texture for that corridor in
Paint.net and giving it wooden or concrete walls, floors, or whatever need be.
Another way is you could have a layer of segment beneath your initial room, and then three quarters up the bottom layer, put a floor
entity with a concrete texture. So when you're dropping from the top layer of segments to the bottom, you're simply dropping just a little, into a crawl space like area, and then you can crawl around beneath the bottom of the top layer on the floor entity.
Just some ideas, hope this helped man.
Cheers
Life would be much easier if I had the source code.