MAP05 - Bone Machine.
Take a mountain outpost it send straight to hell. The "Machine" is a tech base crawling with dangerous creatures. Watch out for new monsters the Spectral Imp and the Hell Rose.
An absent-minded demon has left the vital red door wide-open, leaving the exit room accessible from very early on in the map. Unfortunately, you're likely to want to shut the door yourself when you see what is behind it.