Lichtenstein Cave, Natural monument and prehistoric cave in Osterode am Harz, Germany.

Lichtenstein Cave is a narrow gypsum karst cave about 135 m long in the Lichtenstein hill near Osterode, with winding passages only 30 cm wide in places and a volume of roughly 150 m³. Its small entrance lies on the steep north-northwest slope at about 156 m; the photograph shows a rectangular opening in pale layered rock, framed by dark weathered wood, with a grey-brown door hanging open on the left. Inside, the mouth is a black void.

Three Osterode amateur researchers found the cave in spring 1972 while searching for a secret passage beneath the former Lichtenstein castle; it was first called Rotkamphöhle. In 1980 cavers pushed through a sediment-blocked fissure and reached five chambers holding thousands of human and animal bones, bronze objects and Urnfield culture pottery. The cave was declared a natural monument in 1974.

The cave's original name, Rotkamphöhle, was changed to Lichtensteinhöhle after the hill above it. The bones belong to the Urnfield Culture, whose usual rite was cremation; this site is one of the few with unburnt remains. A 13-metre replica section in the Iberger Tropfsteinhöhle visitor centre can be walked and partly crawled through.

The cave is closed to the public; the small entrance lies in woodland on the lower north-northwest slope of the Lichtenstein hill, about 156 m above sea level. A 13-metre section can be walked and partly crawled through in a replica at the Iberger Tropfsteinhöhle cave centre near Bad Grund, roughly 11 km to the north-northeast.

The cave lies at about 156 m on the steep north-northwest slope of the Lichtenstein hill, below the ruins of Lichtenstein Castle. Its entrance is small and was sealed with a door by its discoverers on 21 March 1973; youths broke it open on 10 October 1974, and it was renewed afterwards.