The single-nave St. Martin’s Church was built by Johannes Orgas, the bishop of Saare-Läänemaa (Ösel-Wiek), in the beginning of 16th century. His shield is located in the church wall, above the north portal. The oldest artefact inside the church is a Gotland-style baptising stone. Also valuable are the altar wall and Empire style pulpit. The church’s collection of 17th-18th century epitaph coat of arms is third in size after Tallinn Dome Church and Niguliste Church.
Reference: Visit Estonia
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.