Tomb of Horrors - 1st Edition AD&D
When you think of the stereotypical D&D dungeon crawl through a dark place filled with deadly traps and menacing monsters, you're imagining Gary Gygax's Tomb of Horrors, even if you don't know it. The tomb of the demilich Acererak would turn out to be one of the most challenging modules of all time. Filled with complicated puzzles, the module has the reputation of being the most deadly in the history of D&D. It's been revised for multiple editions of the game, most recently in 2010 for 4th Edition.