Dwimorberg was part of the White Mountains, which was situated at the head of the valley of Harrowdale. Dunharrow stood above a cliff on the valley's eastern side, parallel to the Dwimorberg Mountain itself. Beyond Dunharrow was a forest of pine wood and fir, known as the Dimholt.
The Dimholt itself contained a small glen, which held a standing stone that lay in front of a doorway that led to the Paths of the Dead. The paths led under the Dwimorberg mountain and were in the Third Age haunted by the spirits of Atani that dwelled forever. The Men of the mountain swore an oath to Gondor and Isildur, the then King of Gondor. But when called upon to fulfill it, they did not and so Isildur cursed them, never to rest until they had fulfilled their oaths.
Aragorn eventually allowed them to finally fulfill their oath, and they were released to go in peace. After the great events at the end of the Third Age, Dwimorberg was haunted no longer.
Dwimorberg was a Rohirric word that meant 'haunted-mountain'.