Naxxramas

[Magictroth]

Naxxramas is a giant necropolis floating over Wintergarde Keep, in Dragonblight. It has the questionable honor to serve as the seat of one of the Lich King's most powerful officers, the dreaded lich Kel'Thuzad.

The instance has been redesigned for 10 & 25-man raids. It consists of four different wings which, when cleared, grant access to the Frostwyrm Lair (a fifth & final wing). Progression is non-linear - raids may select their own path to the final lair.

[Magictroth]

The 10-man version will usually require 2 tanks, 3 healers and 5 dps, in mostly level 80 blues.

More info:

http://www.wowwiki.com/Naxxramas