The English name of this 1128 m high mountain is The Obsidian Skerry. It is situated some distance east of the infamous volcano Hekla. It is accessible by 4WD vehicles from the north and south. On a fine day the view from the mountain is excellent. The surroundings of the mountain are a very colourful rhyolite area with many hot springs, steam vents, boiling mud pits and ice caves, where there is geothermal activity under the ice.During the winter months Hrafntinnusker is only accessible by Super Jeeps.