There's a lot of it, even counting only the parts they visit, and none of the gravity-free sections that Kers points out but doesn't enter. There are more windows, some looking down, some looking up. There are long corridors. Lots and lots of long corridors. There is a magnetic train suspended in a vacuum tunnel, for getting from place to place on the ring quickly; in fact there are four such tunnels and a considerable number of individual train cars.

And there are living quarters, which is where they end up.