Underville, Xana's homeworld, is a set of 2⁶⁴ cubical rooms. That's about 1.8×10¹⁹, which seems like an immense number, but it's not incomprehensibly huge; the total volume of Underville is about 0.8 times the size of the moon. The rooms connect at the edges, and each room connects to four others, but not in any way that makes coherent Euclidean sense. Deep Down Town is the part of Underville Xana's from, and it's the set of rooms along the path from Elseways to Inver City, plus their neighbors.

@bj only four others--is it a 2d grid, or are there multiple levels and some rooms just don't have, say, an east exit in favor of an up exit
-F

@Felthry The latter. Every cube has four exits to other cubes somewhere in its walls, but they don't have to be in any specific place. Since the whole thing is a non-Euclidean mess anyway, you can get rooms with all four doors on a single wall and all leading to places that "should" overlap.

@Felthry One rule that is consistent, though, is that there are no one-way doors. If you go from room A to B through a specific door, then going backwards will always take you back to A.