Mardenholde Keep is the fortress keep within the town of Hearthglen, currently held by the Scarlet Crusade. It is the location of Highlord Taelan Fordring, and is heavily guarded by soldiers of the Scarlet Crusade.
Before the destruction of the Third War and the rise of the Scarlet Crusade, Mardenholde was the seat of Lord Tirion Fordring, the governor of the Alliance principality of Hearthglen. It was a bustling center of regional commercial activity and was one of the bastions of the Alliance that never fell to the orcs during the war. Although the keep is still intact, its original image as a bastion of hope has long since been destroyed.
Mardenholde and Hearthglen will be reclaimed by Tirion Fordring in Cataclysm.