An Adventure for 4th to 5th level characters by Monte Cook.
From the back cover:
Years ago, enigmatic figures known as the Triune created a strange temple and set themselves up there as gods. Though they wielded great
magic, their religion eventually disintegrated and their temple fell into ruin. Wise ones speak of unusual magic, bizarre riddles, and ritualized tests within the place. But a powerful magic item called the strand of tears may still be lost in these mysterious ruins...
The challenge of The Temple of Mysteries: In Media Res lies not just in overcoming foes in combat,but in solving puzzles and dealing with unique roleplaying situations.This difficult dungeon will challenge even the most experienced players. The Temple of Mysteries is intended to serve as a one-shot adventure