Written records mention the castle in Danków for the first time in the 15th century. According to the descriptions, it was situated on a flat yard which, due to a steadily rising slope located 1.5 km away from the castle itself, lay 30 m higher than the courtyard. A church was constructed in close proximity to the castle, according to some sources as early as in 1550. The church underwent major alterations in the years 1630-1650 and has survived to this day.
Starting from the 17th century, Danków was the seat of the Warszycki family, and it is believed that the first owner was Andrzej Warszycki, Voivode of Podlaskie Voivodeship. The castle underwent major alterations in 1632, when it was governed by Stanislaus III Warszycki; the bastion fortifications were built then. Following the death of Stanislaus III, the Warszycki family kept the castle for a short time, and at the beginning of the 18th century, the estate was taken over by the Pociej family, and then the Wessel family. Due to the loss of its major strategic and defensive importance, starting from 1823, the structure was falling into ruin; its shape of an elongated quadrangle with two gates remained fairly discernible. Nearly 30 years later, no trace was left of the castle structure — the stone walls were dismantled by the locals. One of the unfavourable changes was the formation of another entrance passage in the structure of the west bastion in the 2nd half of the 20th century. The first works aimed at protecting and preserving the site were carried out in the 1970s. Detailed archaeological and architectural research was conducted within the defensive fortifications. The walls were protected with brick siding on the south, west, and east sides (the last being the waterfront).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.