Udûn was the deep valley in the northwest of Mordor, formed at the meeting of the Ered Lithui and the Ephel Dúath. Its northern entrance was guarded by the Morannon and its southern entrance was guarded by the Isenmouthe. The fortress Durthang stood in the northern Ephel Duath, on the slopes above Udûn.
- ↑ J.R.R. Tolkien, The Lord of the Rings, The Return of the King, "Map of Rohan, Gondor, and Mordor"
- ↑ J.R.R. Tolkien, "Unfinished index for The Lord of the Rings", in Wayne G. Hammond and Christina Scull (eds), The Lord of the Rings: A Reader's Companion, p. 297
- ↑ J.R.R. Tolkien, The Lord of the Rings, "Index"