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....