Name of site - Ustra Medieval Fortress, an archeological monument of national importance.
Location - village of Ustren, Dzhebel Municipality. It is located about 5 km notheast of Ustren and 3 km southeast of Lebed village.
Access to site - There is natural forest road that leads to it. There are two ways to reach the fortress. One is to follow the sign at the turnoff before Ustren village. The other is to follow a path around 1 km before Lebed village. This path passes nearby the mouflons breeding ranch. Note: The road from Lebed village is easier to climb but it is harder to find the fortress this way. Local people can always help. The other approach is from Ustren village. It is signposted.
Description of site - the fortress is situated on a high, elongated ridge of the same name. The peak is 1015 m high. The area is 1.2 acres. The fortress wall is 113 meters long and has a U-shape. At ground level the wall is 2.8m wide and the top it is 1.75 meters. Some places are preserved to a height of 8 meters. The fortress had three defensive towers - one semi-circular and two rectangular with three floors each. The first floors were underground and were used for water storages. They were coated with stucco, obtained by mixing mortar with crushed bricks and large pieces of pottery. The towers had internal staircases, only some of which have been preserved. The entrance was from the east. Door opened vertically