Coloma castle was built around 1515. It is a square building with square corner towers and a pear-shaped roof and surrounded by a moat. The castle has been completely restored and serves as a municipal cultural center. In the castle park are some interesting buildings such as the former carriage house of 1731 (now a cozy tavern) and a garden pavilion with stair tower. The Rose Garden of Coloma is the largest in Europe. The garden has an area of 15 hectares.
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.