Thandol Valley was a region between the ruins of the ancient dwarven city of Dun Modr in the southern area of the Arathi Highlands and Dun Algaz north of Grim Batol in the northern area of the Wetlands during the Second War. The three narrow land bridges passed through a canyon in between the two outposts. Thandol Span would later be built across the canyon. The canyon may be the valley that gives the area its name.
During the Second War, after their defeat at Dun Modr, the orcs were forced to retreat south across the Thandol Valley to their secondary outpost at Dun Algaz. Lord Lothar intended to push them further back into Khaz Modan and ordered an attack on their base in Dun Algaz, having it destroyed.