Cult of the Cave Worm is a Pathfinder adventure for four 5th-level characters, continuing the Sky King's Tomb Adventure Path, a three-part monthly campaign in which a group of adventurers travel deep underground to discover a legendary dwarven king's tomb, seek subterranean treasures, and heal millennia-old injustices -- all while stopping an ambitious villain from weaponizing those same discoveries. This adventure also includes a study of cave worm ecology, a gazetteer of the duergar city Hagegraf, potent relics, and several monsters to threaten underground explorers.