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. Gary Gygax's opening movement, Village of Hommlet, came out as a standalone in 1979, which sold well itself; but due to Circumstances the other modules didn't follow. After several years of TSR teasing Frank Mentzer fixed it all up and published the whole thing (including Hommlet) as a single book with a map booklet, in 1985. That's the one that justified the hype.
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. The Temple turns out to be the prison for demoness Zuggtmoy, whose cult has been manipulating the others'.
ToEE has since received multiple different iterations across different editions. Monte Cook did a sequel, Return to the Temple of Elemental Evil. This brings in Tharizdun as well. Most of that takes place in the Temple of All-Consumption; a stripped-down Temple of Elemental Evil serves as the endgame here.
A 3rd Edition Dungeons and Dragons based video game version was released in 2003. It is best known for having the most accurate adaptation of 3E rules to a video game and being an excellent example of turn based combat, and as being a schoolboy's lesson for decent quality-control due to its massive game-breaking BUGS. Tim Cain actually owns the rights to the source code for it and Arcanum and wants to release it (and fix the bugs), but his contract won't let him because it would allow for bypassing the CD check DRM that was broken the week it came out and sold without since 2010.
Reprint and 5e Conversion
As with a number of other modules, Wizards of the Coast licensed Goodman Games to do both a reprint and total conversion of the T series of modules (T1-4) to 5th Edition. With childish glee, Goodman Games announced the remake as "Original Adventures Reincarnated #6" in early 2020 with the hopes to get it out by Christmas but due to ongoing global issues it may not release it until early-to-mid 2021.
Due to just how big a T1-4 conversion to 5e is, this is the first remake by Goodman Games that is going to be sold in two books sold together in a slipcase. Fans now wait with bated breath to see how well the conversion is and, if shit, will at least have a very beautiful reprint of the original modules at least.