My favourite roguelike game, T.O.M.E. has a "Lost Soul" mode, in which you start off as a dead soul, freshly arrived in the Halls of Mandos. Armed only with some starting adventurer's gear, the goal is to make your way back to the real world so you can live your life again. Except that the monsters inhabiting the Halls are the kind who ordinary adventurers will only be facing once they've reached level 50 - and you're right at the bottom of about a hundred dungeon levels.
The D&D equivalent would be trying to survive as a 1st level wizard in a dungeon filled with ancient red dragons, balors, pit fiends and a few tarrasques for good measure. You die time and time again - dozens upon dozens of characters consigned forever to oblivion. But every so often you manage to get a kill, of some lowly denizen, which nevertheless gives you enough XP to gain sometimes five levels at a time. And these little rewards keep you interested. Until you turn the next corner and that character gets splatted and you have to start all over again.
I want to make a campaign based on this.