Gudsberga Abbey (Gudsberga Kloster) was a Cistercian abbey established in 1486. It was the last Cistercian abbey in Sweden. Gudsberga owned farms, manors, foundries and mines until 1527, when it was reduced to the Crown during Reformation. In 1538 and 1544 King Gustav Vasa ordered to send silver from abbey to Stockholm. It was demolished later. Today some stone foundations remain and there is a museum exhibiting the forge of abbey.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.