Ustra is the most picturesque fortress in the Rhodopes. It stands on a steep rocky peak, which offers an incredible scenic view to the Eastern Rhodopes. Ustra was built in the Middle Ages, about 10th century. It was ruled mainly by Byzantines, and only rarely by Bulgarians. It was used for control and defense of the main road. A part of its eastern wall, as well as the whole foundation of the buildings and the defensive towers, are well-preserved nowadays.