Basic premise is, that a lot of species live in pyramids in space that have been built by an unknown race. They travel with a rail system. The main protagonist is then "tasked" with repairing the pyramids. (at this point I am not sure anymore if they were pyramids)
Edit: The pyramids are in space rather huge, but only a small percentage is livable as the rest is locked of. The main character is a female police officer on this space station. At one point she gets stuck in an elevator and brought to one of the locked floors. There she meets one of the people repairing the pyramids. He was dying and she got the quest/job/responsibility to repair the building. She can travel through the whole pyramid through a door in her room.
The tram system was basically baskets travelling on a track. That was slow. The real was was to travel in the track.
An unknown alien race was trying to destroy the buildings and she starts defending it.
It turns out the cook of her favorite restaurant was one of the builders.
At this point this is all I know.