The Dwimorberg in the White Mountains (slightly conjectural)

Among the White Mountains, at the head of the valley of Harrowdale, the ancient hold of Dunharrow stood above a cliff on the valley's eastern side. Beyond the hold to the east was a forest of pine and fir, the Dimholt, that shrouded the lower slopes of a brooding black mountain. That was the Haunted Mountain, named Dwimorberg in the language of the Rohirrim.

In the depths of the dark Dimholt wood, at the entrance to a glen, stood a single standing stone. Behind that stone, in the depths of the glen, was a Dark Door, the entrance to the Paths of the Dead. Those Paths beneath the Mountains had been haunted by the betrayers of Isildur throughout the Third Age. The Dead that dwelt beneath it gave the Haunted Mountain its name, but Aragorn allowed them to finally fulfil their oath to his ancestor, and so have peace. After the great events at the end of the Third Age, then, the Dwimorberg was haunted no longer.