In the north-west of the village of Lengenfeld unterm Stein in Eichsfeld in north-western Thuringia rises the 401-metre-high hilltop of Bischofstein Castle.

Built in the 18th century, the castle was used as a summer residence and seat of the bailiffs of the Mainz Elector Johann Friedrich Karl von Ostein (1689-1763). It was built from the stone material of the former Stein Castle, which was first mentioned in 1234 and destroyed in the Thirty Years' War.

After secularization, the castle was used as a manor and then converted into an educational home. During the GDR era, it was an FDGB recreation home, and after reunification there were various attempts to create a boarding school and a meeting place for young people from all over Europe. After an eventful history, the baroque castle is now home to a care center.