In the Middle Ages, Den Dool castle served as a summer residence for the abbots of the Abbey of Sint-Truiden. The first mention is from 1282. Around 1340 the first abbot, Amelius van Schoonvorst, was there as a refugee during the wars of Liège against prince-bishop Engelbert van der Mark. In 1361 the castle and farm were burned down by knight Hendrik van Halbeek. The castle was restored between 1443 to 1470. and again in 1522. It became a fortified mansion with a ring wall with towers and a deep canal.
Further enhancements were carried out by Abbot Hubertus van Sutendael (1638-1663), who had an entrance gate built in 1621 and a castle chapel in 1649. The complex was transformed in a classical style in the 18th century.
Den Dool was occupied by German soldies in the first and second World Wars causing damage to buildings. Since 1994, De Dool Castle Brewery has been located in the farm of the castle. Various restoration work was carried out in the following years.
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.