Gnipahellir, in Norse Mythology, is the overhanging cave at the entrance of the Norse Underworld. Garm, the hellhound, is said to be chained here. Norse mythology, Viking mythology or Scandinavian mythology refer to the pre-Christian religion, beliefs and legends of the Scandinavian people, including those who settled on Iceland, where the written sources for Norse mythology were assembled. ... In Norse mythology, Garm was a huge four-eyed dog that guarded Helheim, the land of the dead, living in a cave called Gnipa. ...