The Temple of Mysteries: In Media Res
A dungeon of tricky puzzles, ancient magical secrets, and more than a few lingering mysteries, designed to be played as a standalone adventure and not incorporated into another campaign.
Six adventurers descend into the Temple of Mysteries to find a mystical artifact called the Strand of Tears. Seems straightforward enough, except that some of the party may not be who they say they are. In fact, none of the party may be who they say they are. Not only that, but they might not be who they don't say they are, either!
Worst of all, they're trapped in the ruins of an underground temple specifically designed to keep people from proceeding unless they're proficient in puzzle-solving...and there may be doppelgangers on the loose.