Lengsfeld Castle, also known as Boineburg Castle, was a fortification built in the Middle Ages in the Feldatal, on the outskirts of Stadtlengsfeld. In order to secure their possessions, the monastery Hersfeld had a castle built in 1125 in Lengsfeld and there the lords of Lengsfeld perform their ministerial services. The castle was extended after the decline of the Frankensteiner on endeavors of the Fuldaer abbots and built a protective wall as well as a moat. The moated castle came from 1523 until the end of World War II in the possession of those of Boineburg. The moats were filled in at the beginning of the 19th century. During the Second World War, prisoners of war and forced laborers were housed in the castle. In 1950, a convalescent home was opened in the castle and expanded in the following years. In 1991, the sanatorium was built by Dr. Ing. Becker hospital company taken over. Today's Burgklinik functions as a specialist clinic for psychosomatics and oncology.