Södertuna is a medieval castle located on a small island in Lake Frösjön in Gnesta Municipality, Sweden. It dates to the 14th century and is now a luxury hotel and conference center. The main building is of medieval origin, but was updated during the 17th century and the late 18th century. The last major renovation was in 1892.
It has belonged to members of several families: Sparre, Lovisin, Palmenfelt, Ehrensvard, Wachtmeister, Adelborg, and von Eckermann.
The castle and the park were split off in 1985 by the von Eckermann family. The new owners, together with an additional couple of Norwegian investors, made the palace into a hotel and conference center, which was inaugurated in 1986 by Princess Christina. In 2007 the castle was sold to the Åström family, which also operates Dufweholms Manor Inn and Gripsholm.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.