Udun is a narrow valley in the northwest corner of Mordor, where the Ash Mountains meet the Mountains of Shadow. At one end of the valley is Cirith Gorgor and the Black Gate of Mordor, at the other end of the valley was the narrow pass called Carach Angren. There were many Orc-holds, armouries and tunnels in the mountains on either side of the valley, used by the troops guarding Morannon.