The mountain where the Paths of the Dead are located is Dwimorberg.
Dwimorberg, meaning the Haunted Mountain, is a peak of the White Mountains in Tolkien’s Middle-earth. The Paths of the Dead begin at the Dark Door beneath the mountain, passing through a haunted underground route from Dunharrow in Rohan toward Blackroot Vale in Gondor.
The passage is guarded by the Dead Men of Dunharrow, the oathbreakers who refused to aid Isildur during the early history of Gondor. Isildur cursed them to remain bound to their oath until a true heir of the king summoned them. Their presence made Dwimorberg one of the most feared places in Rohan.
In The Return of the King, Aragorn, Legolas, Gimli and the Grey Company enter the Paths of the Dead. Aragorn invokes his descent from Isildur and commands the Dead to fulfil their ancient promise. They later help defeat the Corsairs of Umbar before their oath is released. Dunharrow is the approach and refuge, while Dwimorberg is the mountain itself; Mindolluin is the mountain beside Minas Tirith.