Classic old AD&D module from Gary Gygax:

AN ADVENTURE SET ON GREYHAWK’S WORLD FOR CHARACTER LEVELS 5-10

This special module is a combined wilderness and dungeon adventure scenario. It contains background information, referee’s notes, encounter keys,outdoor and dungeon level maps, and new monsters and treasures. While it is designed to interface with LOST CAVERNS OF TSOJCANTH, this module is capable of standing alone. Likewise, while it is placed within the Greyhawk Campaign, it can easily be adapted to play in any individual campaign which employs the ADVANCED DUNGEONS & DRAGO game system.

… The Temple was built in a previous age, a secret place of worship to Tharizdun, He of Eternal Darkness …