Udûn may refer to:
*
Udûn, Iron Mountains, also called Utumno, the underground fortress of Morgoth in the Age of the Lamps, before the First Age of Middle-earth in the writings of J. R. R. Tolkien
*
Udûn, Mordor, the plain by the Black Gate at the northwestern point of Mordor in the Third Age in the writings of J. R. R. Tolkien
*
Udûn (''The Lord of the Rings: The Rings of Power''), an episode of the television series, named after the plain in Mordor
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