Burg Losenstein, Medieval castle ruin in Losenstein, Austria.

Burg Losenstein is a ruin on a 60-metre dolomite rock above the village of Losenstein. It consists of a 2,200 m² main castle and, about 45 m west, a 400 m² outer bailey. The palas, probably the oldest part, stands on rock and shows a transition from Romanesque to Gothic window arches.

The Styrian Ottokars built the castle around 1150 to guard the route into Styria; it was first documented in 1170. In 1252 Dietmar of Steyr received it from King Ottokar II of Bohemia in exchange for the city of Steyr, and his descendants, the Lords of Losenstein, held it until 1692. It then passed by inheritance to the Auersperg family, who sold it to Upper Austria in 1905.

The name Losenstein comes from Dietmar of Steyr, who received the castle in 1252 and called himself Lord of Losenstein. The castle theatre group of Losenstein has staged plays in the ruins, and the site now includes the Burgfelsen climbing area. Child-friendly signs explain the ruins to visitors.

The ruins are freely accessible throughout the year at no cost. Parking is available at Burgstraße 27 in Losenstein.

The castle rock is a climbing area, and the ruins have hosted performances by the Losenstein castle theatre group. Child-friendly signs explain the site's history to visitors.