Surtshellir (Icelandic pronunciation: ​[ˈsʏr̥(t)sˌhɛtlɪr̥]) is a lava cave located in western Iceland, around 60 km from the settlement of Borgarnes. Approximately a mile in length, it is one of the longest such caves in the country. It was the first known lava tube in the world, at least by modern speleologists, and remained the longest known lava tube until the end of the 19th century. While mentioned in the medieval historical-geographical work Landnámabók, Eggert Ólafsson was the first to give a thorough documentation of the cave in his 1750 travels of the region. It is named after the fire giant Surtr, a prominent figure in Norse mythology, who is prophesied to one day engulf the world in the fire of his flaming sword.