The Pacov Highlands rise gently south of Chýnov. The highest point of the highlands is Choustník (680 metres above sea level) which is dominated by a castle named after the hill.

This mighty castle was founded in the mid-13th century and only ruins of walls and two towers have remained of it. The ruins boast an unusual layout (it is a rare example of a double castle). The castle was owned by the Rožmberks from 1355 till 1597 when Petr Vok sold it; in 1614 the castle was abandoned. The core of the castle is situated on a steep rock; visitors who climb up the stairs in one of the towers are rewarded with a beautiful view from a height of 18 metres; weather permitting one can see as far as the Šumava Mountains or the Brdy Hills.