Bladenhorst castle was first mentioed in 1266 as the residence of the lords of Blarnhurst lived there. At the beginning of the 14th century it became the possession of the family of Düngelen. In 1338, Rötger Düngelen made the castle available to the Duchy of Cleves to use in the event of war. Through marriage, in 1496 the castle passed to Philip of Viermünden. From 1624 to 1881 it was inherited by the Westphalian noble family of von Romberg.
The structure originally consisted of four wings. The gatehouse is the oldest part of the building, the chapel dates from 1332. The castle as it stands is in the style of the Renaissance - coming from its rebuilding between 1530 and 1584.
Today castle is still inhabited, and privately owned, consequently there are no public tours or visits, some parts of the castle are rented out to private individuals.References:
First record of Kastelholma (or Kastelholm) castle is from the year 1388 in the contract of Queen Margaret I of Denmark, where a large portion of the inheritance of Bo Jonsson Grip was given to the queen. The heyday of the castle was in the 15th and 16th centuries when it was administrated by Danish and Swedish kings and stewards of the realms. Kastelhoma was expanded and enhanced several times.
In the end of 16th century castle was owned by the previous queen Catherine Jagellon (Stenbock), an enemy of the King of Sweden Eric XIV. King Eric conquered Kastelholma in 1599 and all defending officers were taken to Turku and executed. The castle was damaged under the siege and it took 30 years to renovate it.
In 1634 Åland was joined with the County of Åbo and Björneborg and Kastelholma lost its administrative status.