Well worth a visit. Its history is unclear but it is certainly one of Afghanistan's most important historical buildings. Possibly dating from Zoroastrian times, the remains are now under a protective roof, and are worth the bumpy 2-km drive from the main Balkh - Mazar road. Head south from the centre of Balkh, cross the main east-west road and keep going. After 500 metres you'll see a sign (in English) telling you to turn right.