Tynnelsö estate was first mentioned in 1282. Since 1306 it belonged to the Diocese of Strängnäs. During the 1490s bishop Kort Rogge built the first stone castle and the first floor is still the original. In 1522 Tynnelsö was acquired by Gustav Vasa and it belonged to the royal family until 1636, but was again later returned to the crown (during the Great Reduction in 1681). The current square-formed castle was built to the present appearance in the 1590s. In the 18th century Tynnelsö castle was abandoned and left to decay. The major restoration was made in 1826-1827.
Today the castle is closed due the restoration, which should be started in future. The surrounding garden includes lot of lime trees and a villa built in 1876.
References:The Gravensteen is a castle in Ghent originating from the Middle Ages. The name means 'castle of the counts' in Dutch. Arnulf I (918–965), Count of Flanders, was the first to fortify this place, building a medieval bastion on this high sand dune, naturally protected by the river Leie and its marshy banks. This bastion consisted of a central wooden building and several surrounding buildings, also in wood.
In the early 11th century, the wooden building was replaced by a stone residence, consisting of three large halls that made up three storeys, connected by a stone stairwell. The monumental stone staircase, the light openings, the fireplaces built into the walls and the latrines were signs of considerable luxury and comfort in those days. There was probably also a tower.