The ruins of the Kirnburg are located at 382 m above sea level on the mountain of the same name (Kurinberc since 1219) above Bleichheim above the confluence of the Kirnbach in the valley of the Bleiche. The castle was the administrative center of the Usenberg and later the Upper Austrian rule of Kenzingen and Kürnberg. The builder of the Kirnburg is Rudolf I von Üsenberg in the early 13th century.
The 60 x 80 m area of the upper castle and its outer bailey is secured with several neck ditches to the south. This spur was once used to access the weir system. The oldest element in the center of the castle is the square tower built shortly after 1200 from humpback ashlars. The original complex also included a curtain wall and a gate, in which a certificate was issued in 1219.
In 1352 Friedrich von Üsenberg sold the castle to Heinrich IV. Von Hachberg. During this time the shield wall and other buildings were built. In 1515 it came - dilapidated and not habitable - into the possession of the knight Wolf von Hürnheim, who probably carried out the last construction work. At that time the hall was redesigned and equipped with a splendid tiled stove. After the destruction in 1638, the castle fell into disrepair and served as a quarry, so that the former building stock is only partially legible today. (van Akkeren / Jenisch 2019)