Rheinstein castle was constructed around 1316-1317. It was important for its strategic location. By 1344, the castle was in decline. By the time of the Palatine War of Succession, the castle was very dilapidated. During the romantic period in the 19th century, Prince Frederick of Prussia (1794–1863) bought the castle and it was rebuilt.
In 1975 the opera singer Hermann Hecher bought the castle. It's due to him that Rheinstein Castle became again one of the centres of attraction in the Rhine Valley. Around the apartment tower from the 14th Century you find neo-Gothic sets, turrets, terraces and iron stairs. Inside are stained glass windows and mural painting as well as a Renaissance fire-place and stylish furniture.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.