On Cimmeria, a large monolith near the stargate was left by the Asgard to protect the planet. It scans those who arrive through the stargate and detects the Goa'uld, known as Etins, sending them to a labyrinth deep underground. The Hall of Mjollnir, a passage within the underground maze, leads to Thor's Hammer, a doorway that is the only exit. Thor's Hammer destroys any Goa'uld attempting to pass through it, leaving only the host alive. SG-1 destroyed Thor's Hammer to free Teal'c from the maze, leaving Cimmeria vulnerable to attack. Following an invasion by Heru'ur, the Asgard restored Thor's Hammer, which now makes an exception for Teal'c.
Cross Reference: Asgard, Cimmeria, Cimmerians, Etins, Gairwyn, Hall of Mjollnir, Hall of Thor's Might, Kendra, Thor
Episode Reference: Thor's Hammer, Thor's Chariot