The remains of the Castle can be visited
Glambeck Castle

The Glambeck Castle Ruin, a medieval lowland castle, rises on the Burgtiefe peninsula in the south of Fehmarn. Although only modest remnants are visible today, it was once a central stage of the island's history and is considered one of the few preserved medieval stone castles in Schleswig-Holstein.
History+
Glambeck Castle was built in 1210 at the behest of Danish King Valdemar II and became the most important historical site on Fehmarn. In 1248, it was the scene of the wedding of King Erik IV's brother Christoph to Margarete Sambiria. The following decades were marked by conflicts between the Counts of Holstein and the Danish kings. In 1307, the “Glambeker Comparison” was concluded at the castle, an arbitration by King Erik VI in the conflict between the landed gentry and the Holstein Counts. In 1320, King Christopher II issued the “Oldest Fehmarn Land Law” at the castle. After Johann III of Holstein-Kiel was enfeoffed with Fehmarn in 1326, the Glambeck court was abolished. In 1358, the castle fell to Danish King Valdemar IV, but was recaptured in 1359 by Adolf VII of Holstein-Kiel. In 1416, Erik of Pomerania conquered the island and had the castle captain executed, but the Holstein Counts fought back.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://schloesserrundschau.de/schleswig/schloesser/ostholstein03.html
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 54.4122, 11.2083