Dimmuborgir is a strange place of lava pillars twisted lava tubes and lava caves on the east side of Myvatn. The prevailing theory on its formation is that when fresh lava flowed over a bog or shallow lake the resulting steam explosions caused formation of pillars, lava tubes and caves. Subsequent collapse of the upper layer ("roof") left the vertical lava formations behind. Dimmuborgir is located in a depression, with its main level below the surrounding topography, further suggesting that it formed in a lake.