Kostomlaty Castle, Castle ruin in Kostomlaty pod Milešovkou, Czech Republic

Kostomlaty Castle is a ruin of a bergfrit-type castle on Kostomlaty Hill above the village of Kostomlaty pod Milešovkou. It has a two-part layout: an upper castle with a tall bergfrit tower and two opposing palaces around an irregular trapezoidal courtyard, and a lower bailey entered through a gate protected by a round tower. Parts of the bergfrit, palaces and curtain walls remain.

The castle was built in the early 14th century by the Osek nobles and changed ownership during the Hussite wars. It was abandoned by 1606 and gradually fell into decay.

The castle reflects bergfrit architectural traditions that shaped medieval fortifications across North Bohemia. Its visible remains show how builders designed defensive structures during that period.

The ruins are reached from the village of Kostomlaty pod Milešovkou via a green-marked hiking route. An easier alternative is the vehicle track starting at the road between Kostomlaty and Milešov. The bergfrit tower is again accessible by steep stairs.

In 1841 Josef Fenzel of Kostomlaty built an excursion restaurant in the lower castle, where he displayed finds from the levelling and foundation digging; the inn and the lookout in the great tower vanished in the 1950s, leaving only part of the walls and a cellar.