The castle, or rather a fortified court in Candleston, was founded in the 14th century on the initiative of the Cantilupe family. It could have been built on the site of an earlier building from the 13th century. At the end of the fifteenth century, it was renovated and rebuilt by Mathew Cradock, a constable of castles in Caerphilly and Kenfig, and around 1500 transformations were made in the range of the great hall. Further modifications were carried out in the 17th century, when a new range was added next to the hall building. The lands of the estate in the Middle Ages were covered with sand from nearby dunes and lost their value, but the building remained inhabited until the 19th century. The last person living in the court was Sir John Nichol. When in 1808 he built a new residence, Candleston was sold and used by new owners as a farm. Eventually it was abandoned at the end of the 19th century and fell into disrepair.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.