Back in law school, I was DM to a very eclectic group and they explored one of the most brutal dungeons I've ever created. The difficulty progressed almost geometrically and there was one part where, once you started down a particular hallway, you could only go forward and couldn't really rest. You went through pit traps, teleporting ghouls, symbols of pain, explosive runes, gnolls firing through arrow slits from rooms the party couldn't access, a room that turned into a spinner with blades and then finally a massive battle with the gnolls where they were at the top of a LONG staircase.

Only three of seven party members survived the dungeon, and all but one party member had their alignment forcibly changed to chaotic evil by one artifact or another. And I made them play it. It got nasty. People were reluctant to sleep next to each other.