The picturesque ruin of the Gothic hunting castle Karlův hrádek (also known as Karlshaus or Hrádek) is situated over the left bank of the Vltava at an elevation of 430 m above sea level, by Hněvkovice Reservoir, some 7 km north of Hluboká nad Vltavou.
Karlův hrádek was founded by King Charles IV as an administrative center for the royal territory. The oldest mention dates from 1357. Hrádek was founded in the Old Game Preserve, which today belongs to Hluboká nad Vltavou Castle, and was intended primarily for hunting events. The irregularly shaped, roughly triangular castle was surrounded on all sides with a massive moat and rampart. It was probably without a tower, and access was gated in the passageway of the northern wing, where stone slabs can be seen to this day. The castle chapel has been largely preserved. Hrádek declined under the reign of Wenceslas IV, and was reported abandoned from the late 14th century onward.
Karlův hrádek can be reached along the red walking trail, about 8 km from the Hluboká-Zámostí railway stop. It is about 2.5 km from Purkarec in the opposite direction. The history of the castle is connected with several local legends. According to one of them, there should be a cellar full of wine somewhere under the castle, guarded by a large angry dog.