Kastelholm castle was first mentioned in Chronicles in 1388 the House of Kastelholm". The exact date of Foundation of the castle, however, is unknown. From the end of XV century the castle was the administrative center of the archipelago and played an important strategic role, and was a hunting castle of the Queen of Sweden.

In the present appearance of the castle is a complex architectural complex, was built and widened in the period from the late fourteenth to mid-seventeenth centuries In 1745 in the castle there was a devastating fire. Only in the twentieth century it was restored and opened to the public.

Next to the castle opened two museums. One State prison Museum Vita björn, located in an old prison building. Second, is the Museum under the open sky Jan Karlshagen where you can see over twenty traditional åland houses and mills of the nineteenth century. On the old coaching Inn, the visitors are treated to local food.