Halleberg is the northernmost one of the twin mountains Halleberg and Hunneberg. It stretches towards Lake Vänern to the north and is separated from Hunneberg by a valley 500 metres wide. The northern part of the mountain is called Hallesnipen. The highest point of Halleberg is at 155 metres above sea level. Like Hunneberg, Halleberg consists of sandstone, alum shale, and dolerite and lacks the limestone and clay shale layers found in most other table mountains. The dolerite layer is very thick, however, up to a maximum of 60 metres. The dolerite slopes give the mountain its characteristic appearance and favour a very special flora and fauna.
Halleberg is regarded by some as the site of Valhalla, the residence of the gods in Norse mythology. One part of the mountain is still called Häcklan, derived from one of Odin’s names: Häcklaman.