The Landnama Saga derives the name Surtshellir from a huge giant called Surtur, who made his abode in the cave; but Olafsen believed that the name merely meant _black hole_, from _surtur_ or _svartur_, and was due to the darkness of the cave and the colour of the lava: in accordance with this view, it is called _Hellerin Sortur_, or _black hole_, in some of the earlier writings.

The common people are convinced that it is inhabited by ghosts; and Olafsen and his party were assured that they would be turned back by horrible noises, or else killed outright by the spirits of the cave: at any rate, their informants declared they would no more reach the inner parts of the cavern than they had reached the traditional green valley of Aradal, isolated in the midst of glaciers, with its wild population of descendants of the giants, which they had endeavoured to find some time before.[109] The cave is in the form of a tunnel a mile or more in length, with innumerable ramifications, in the lava which has flowed from the Bald Yoekul.

It lies on the edge of the uninhabited waste called the Arnavatns-heidi, in a district described by Captain Forbes as distorted and devilish, a cast-iron sea of lava.

The approach is through an open chasm, 20 to 40 feet in depth, and 50 feet broad, leading to the entrance of the cave, where the height is between 30 and 40 feet, and the breadth rather more than 50.

Henderson found a large quantity of congealed snow at this entrance, and along pool of water resting on a floor of ice, which turned his party back and forced them to seek another entrance, where again they found snow piled up to a considerable height.