[nauful]

Depending on the technology used it may be trivial to extremely difficult.

For most additive geometry constructed maps, cracks can form to create collision holes which otherwise look solid, or the map may not be entirely closed and have a gaping hole into the void. This is very difficult to get right.

For maps which carve out empty space from solid space and then add geometry back (subtractive, such as Unreal), there may be cracks caused by numerical imprecision but collision errors here are relatively rare.