Pustý hrádek, Fortified tower in Žlíbek, Czech Republic.

Pustý hrádek is a medieval fortified tower in Žlíbek that forms part of the defensive system around Kašperk Castle. The structure is built with thick stone walls and sits in a location where the surrounding land could be easily watched.

Pustý hrádek was built as an outpost bastion of Kašperk Castle on a hill about 400 metres east of it, to stop attackers from firing on the lower castle from above. Its earliest possible construction date is the turn of the 1470s and 1480s, when the Šternberks held Kašperk and from 1487 the Švamberks; the only written mention is from 1608. Archaeology documents its use in the 15th century.

The tower reflects medieval building methods that were common in this region and how people once protected their lands. When you visit, you can see how the walls were constructed and which areas could be watched from this vantage point.

A yellow-marked hiking trail leads from Kašperk Castle to the ruin, about 400 metres east of the castle. The site is freely accessible, with no guided tours, and the walk ends on a hilltop with a view of Kašperk and the Bohemian Forest.

The surviving north wall keeps the 28 × 28 cm pockets that held the floor beams of the second storey; their small span shows the floor was built for heavy loads. The building ended in a large fire that burned the beams down to the bottom of these pockets.