Koznik Fortress is located on the top of the hill 8 km west of Aleksandrovac. It is not known who founded the city, but it is assumed that it was done by the Celts. The city had an important role in Nemanjic period. It was located on the caravan route to Dubrovnik. Despot Stefan Lazarevic gave it in 1405 to Serbian nobleman Postupovic Radic, along with 70 villages.
The city has a polygonal base with walls reinforced with four-squared towers. Under the south side of town a village probably stretched, where remains of one tower are. The town had a main gate near the northeast tower of the north wall, with the auxiliary entrance in the northwest tower.
Donjon tower is located at the highest point of the city, about 921 m above sea level, in the middle of the northern wall. It was a four-sided tower, with the base of a proper square, and sides 9 m long. The wall was about 2 m thick, entered from the south.
Within the city wall remains of several buildings were found, as well as at eastern and western walls. Today, the fortress is generally well preserved. The surrounding hills, though burnt during the wars, are now covered with dense forests due to the work of Nature Conservation. Several forest trails lead to the old town. One of them starts at the village Koznica. Walking takes about 45 minutes.