A dark fortress in southern Mirkwood, used by Sauron as his base of operations during the Third Age while he rebuilt his strength in secret under the guise of the Necromancer. The Wise (Gandalf and the White Council) eventually drive him from Dol Guldur, but he simply relocates to Mordor. The fortress remains a threat throughout the War of the Ring until it is finally cleansed by Galadriel.