Many centuries ago, a castle stood on a limestone cliff a little way from Holštejn. Its name was derived from the German “Höhl Stein” (a hollow rock or stone), since the Hladomorna (Dungeon) Cave, which served as a castle prison, can be found beneath the castle. An access tunnel 14 metres long led to the castle. The cave itself is 17 metres high and 25 x 35 metres in size. The cave floor is covered in a great many rocks which have fallen from the ceiling, and a great many human remains, as well as armour, spurs and other metal objects, have been found in the earth between them. Holštejn Castle was, for a time, held by robber knights who threw their victims into the cave through an opening in the roof. During their investigation of the cave, researchers Jindřich Wankel and Karel Absolon discovered hand-carved steps leading from the opening to the castle square. The Dungeon is today reached through an opening made at the foot of the cliff.
Rare bats – the greater mouse-eared bat and the brown long-eared bat – now hibernate in the Dungeon in the winter months.