Dol Guldur
From t2twiki
Dol Guldur, or the "Hill of Black Magic," was once a peaceful place occupied by the elves of Greenwood the Great. But Sauron's corrupting influence during his "resurrection" after the Last Alliance changed the hill and the woods that surrounded it. Once discovered by the White Council, the Dark Lord retreated to Mordor to gather the forces he now employs against Middle-Earth. Meanwhile, in the heart of the forest of "Mirkwood," Dol Guldur remains a terrible fortress from which Sauron's underling, the nazgul Khamul, launches a campaign against the elven wood of Lothlorien.
The fortress has been a longstanding home of the Sons of Ulfang (save for a brief move to Mordor) as well as a garrison for the Burzgul legion. Beyond these dangers, Dol Guldur also retains tight security measures, using posted guards, roving patrols, a ready bell alarm, and massive gates to keep invaders out as well as prevent unfortunate intruders from escaping with their lives.
In the original works, Dol Guldur sent three waves of forces against the Golden Wood only to be thwarted each time by the combination of Lady Galadriel's ring and the stalwart forces of her husband Celeborn. After the One Ring was destroyed, Lothlorien's forces crossed the River Anduin and lay waste to the dark fortress.
