Naxxramas

An ancient Nerubian ziggurat, Naxxramas was torn free from the ground by agents of the Lich King to serve as Kel'Thuzad's base of operations as he spreads the plague throughout Lordaeron. Other sources say Obrahiim, a great skeletal architect, was pivotal in the conception of Naxxramas, hinting that it was altered or retooled.

Due to Kel'Thuzad fighting a war against the Scarlet Crusade, the Argent Dawn, the Forsaken and the Humans of the Alliance, as well as constant incursions of adventurers from every race and nation into the Scourge-controlled Plaguelands on a daily basis, his forces have been severely taxed to maintain the security of his necropolis. But now the gates of Naxxramas are open, Kel'Thuzad's new forces are rapidly sweeping away all opposition to the Scourge.

After the defeat of Kel'Thuzad in the Eastern Plaguelands, Naxxramas has returned to Northrend and now hovers above the Carrion Fields in the Dragonblight, where it lays siege to the Alliance stronghold of Wintergarde Keep.