Surtshellir is a cave located in Hallmundarhraun lava field in West Iceland about 1 hour drive from the town Borgarnes. It is the longest lava tube in Iceland about 1970 meters long and 8-10 meters high.

Surtshellir is the best known cave in Iceland and is named after the fire giant Surtr, a person from the Norse mythology. The cave is also mentioned in the book of Eggert Ólafsson, Landnámabók. Back in the days outlaws and sheep rustlers used to hide in the cave and steal the livestocks from the farmers in the area. Evidence of their existence in the cave have been found including, bones and signs of human habitation.