Holsteinborg Castle was built by the Trolle family between 1598 and 1651, but has been owned by the Holstein family since 1707. The first count, Ulrich Adolph Holstein, established ten village schools on the estate in about 1710. The first Christmas tree in Denmark was lit at Holsteinborg in 1808, Northern Europe's first savings bank was opened in 1810 and Denmark's first health insurance was available in 1811. Between 1810 and 1825, a total of 14 schools and 12 handicraft schools were built on the estate. Hans Christian Andersen was inspired by his many visits to the castle, where he wrote some of his fairytales, stories, songs, poems and accounts of his travels.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.