The subject of this article or section originates from non-canonical sources. To find out about what is considered "canon" see LOTR:Canon.
The High Fells of Rhudaur are tombs where the nine Nazgûl were buried. Described more as a prison of the dead than as a grave, the tombs are located North of the Trollshaws, within the boundaries of the old kingdom of Rhudaur. The High Fells exist only as part of Peter Jackson's Hobbit trilogy.
Portrayal in adaptations
The Hobbit film trilogy
In The Hobbit: An Unexpected Journey, the tombs are first mentioned by Lady Galadriel during the meeting of the White Council in Rivendell as part of their discussion concerning the rediscovery of the Witch-king of Angmar's Morgul-blade by Radagast in the ruins of Dol Guldur. The tombs are revealed as the location where the Witch-king was buried following the fall of the realm of Angmar, entombed there by the men of the North. The tombs themselves are said to be so dark that they would never come to light. As noted by Elrond, powerful spells lie upon the tombs, which should have prevented the crypts from ever being opened. Saruman however, rules that there is not enough proof that the Morgul-blade actually originated from the Witch-king's grave in the High Fells, and dismisses it.
In the film The Hobbit: The Desolation of Smaug, upon arrival at the forest border of Mirkwood, Gandalf discovers Black Speech graffiti imprinted on an old ruin, coinciding with a telepathic message from Galadriel imploring him to investigate the tombs of the Nazgûl.
When Gandalf reaches the remote tomb of the Nazgûl he finds out that they have been revived. He is joined by Radagast, and it is revealed that the Necromancer cannot be a mere human as the Nazgûl answer only to one master: Sauron. Both of them figure out that the Necromancer is Sauron returned and that he is preparing for war with Azog as the commander of his legions who will begin his attack in the east since Sauron's mind is set upon Erebor. As Gandalf sends Radagast to warn Galadriel of their discovery, Gandalf enters the orc-infested Dol-Guldur and is attacked by Azog.
In The Hobbit: The Desolation of Smaug, upon the urging of Galadriel, Gandalf departs from Thorin and Company to travel with Radagast to the High Fells, in search of evidence concerning the Necromancer's true identity. In addition to the Witch-king, the tombs are revealed to also house the remains of the eight other fallen Ringwraiths. The wizards discover that all nine crypts have been broken open from the inside. After realizing that the Nine have been resurrected from the dead, and have returned to their master in Dol Guldur, Radagast persuades Gandalf, who wishes to rejoin Thorin and Company, to instead investigate the ruins of Dol Guldur, in an effort to confirm their fears regarding the true identity of the Necromancer. In the extended version of the Desolation of Smaug, you see the Witch-King as a dead man, buried by the men of the north. 
- As a plot device, the resurrection of the Nazgûl serves to justify the use of the moniker The Necromancer, as used in the novel when referring to the dark presence dwelling within Dol Guldur, in that a necromancer is someone who communicates with and summons the spirits of the dead.