T1-4: Temple of Elemental Evil
The Temple of Elemental Evil is one of the most famous Dungeons & Dragons adventure modules in the world, after the Tomb of Horrors. It's an epic dungeon delve that revolves around the players breaking into the combined dungeon-temple of the Cults of the Princes of Elemental Evil - the four Archomentals Ogremoch, Imix, Olhydra and Yan-C-Bin, being ultimately manipulated and controlled by the cult(s) of Zuggtmoy and/or Tharizdun. It has received multiple different iterations across different editions.