The Guardhouse is a room found behind a previously locked door in Karazhan and which only became accessible to players during the Scourge Invasion world event preceding World of Warcraft: Wrath of the Lich King. During the event there were several containers, within the chamber, filled with what appeared to be blood. In the center of the room was and the quest item Orders from the Lich King.
However, with Mirkblood slain, the room has been cleansed of his presence and all containers removed. The only thing in the room now is a few tables and chairs.