Udun

Udûn may mean:

In Tolkien's Middle-earth writings

 * Udûn, Iron Mountains, also called Utumno, the underground fortress of Morgoth in the Age of the Lamps, before the First Age of Middle-earth
 * Udûn, Mordor, the plain by the Black Gate at the northwestern point of Mordor in the Third Age

In motion pictures

 * Udûn, an episode in the streaming series The Lord of the Rings: The Rings of Power