Said castle is the Lembecksburg, in fact a medieval ring wall with a diameter of 95 meters and a height of ten meters. According to old lore, it was constructed in the 9th century as a stronghold against the Vikings and is named after the knight Klaus Lembeck who had allegedly been residing there as a steward of king Valdemar IV of Denmark in the 14th century. After breaking his feudal oath, though, Lembeck is said to have been besieged by the king's host.
Valdemar IV of Denmark
Lembeck