The remains of the Kunžvart castle tower above the top of the Strážný mountain (1,115 m) at the Czech-German border about 2 km north-west of the village Strážný. It was practically impregnable stronghold due to its great location enclosed on three sides by rock walls below and by a deep moat.

The name of the  castle comes from the original German name Königswarte (King's Guard). It was probably founded in the first third of the 14th century by King John of Luxembourg for the protection of the frontier of the Czech Kingdom and the trade route Zlatá Stezka (Golden Path). It was first mentioned in 1359, when King Charles IV signed it over as property of the town Vimperk. Its most prominent period was in the 14th century - it was used for levying the duty on the new road from the town Vimperk to the town Passau (Germany). In the first half of the 16th century the castle was completely abandoned and in 1547 it was desolate. In the last quarter of the 16th century it burnt down and it fell to ruins.

Only the 15 metres high residential tower (originally three-storeyed) has been preserved up till the present day.

The yellow marked path leads to the top of the Strážný mountain and to the ruins from Strážný (about 3 km). The blue sign from the small village Horní Vltavice connects the yellow one, which leads to the ruins too (about 9 km).