The fortress is situated on the highest residential part of Hissarluka, which is two kilometers southeast of Kysutendil. The fortress was built in the late 4th and early 5th century. It was reconstructed in the 6th century and has been in use during the First and Second Bulgarian Kingdom and was demolished by the Ottomans in the 15th century. Many and various archaeological finds prove that the fortress continuously used in ancient and medieval times.
Fortress has the shape of an irregular polygon. It has dimensions of 117 m to 175 m, and its surface area is 2.12 ha. The shape of the fortified area follows the slope of the terrain. The fortress was protected by the 14th round, triangular and rectangular towers. There are two gates and five secret entrances. The main and largest port in the eastern wall and close to the main road.
The fortified wall has different widths ranging from 1.6 m to 3 m. The assumed height is 10 meters and the height of the towers – 12 m. The construction technique is called opus mixtum – mixed masonry with alternating layers of stones and bricks from 4 or 5 rows of bricks.
Interesting building techniques, the combination of different construction techniques and materials and excavated archaeological sites from different historical periods define fortress Hisarlaka one of the most important in Bulgaria.
Fortress is a cultural monument of national importance.