The oldest parts of Follingbo Church are the nave and tower. They date from circa 1200 and together form an unusually accomplished example of Romanesque architecture on Gotland. Although lacking in ornamental sculpture, the tower and nave are well-proportioned and unusually professionally executed. The choir is later (late 13th century) and already Gothic in style, and also considered unusual for its kind. The choir replaced an earlier, Romanesque choir with an apse. The current choir instead has a straight eastern wall, adorned with a single tracery window, in which fragments of medieval stained glass panes remain. The sacristy was built in 1820-21.
Inside, the church has a painted ceiling, decorated at the end of the 17th century. Most of the furnishings are also from the 17th or 18th century. An exception is the undecorated baptismal font, which is medieval.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.