A Doom-style map that revolves around a big vaguely hellish rock formation, on which Duke has to "climb" (jump, fall off ledges, etc.) up and down a lot.
A Doom-style map (more abstract and less realistic, among other things) that takes place in some parking lots/garages that have been invaded by the aliens.
After a few days of R&R, Duke Nukem returned to his work for EDF. Now he's a Detective Nukem and his job is to look after the Little Bigville, the little snow town on the edge of nowhere....
This map is based on Big Boo's Haunt from Super Mario 64 but with changes/improvements all over the place (for instance, you can actually see through all the windows, which you couldn't in Super Mario 64).