Mercedarian monastery of San Juan de Poio was built in the 17th century and reflects the taste for combining Classicist and Baroque styles. The first document of the monastery on the site is however much older, dating from 942 AD.
Inside, there is a splendid retable from the 18th century, in Churrigueresque style, and the tomb of St. Trahamunda is in the left-hand aisle (much venerated in the district). The procession cloister (16th century) is also noteworthy, with a Baroque fountain and an original stairway. Also worth mentioning are the library, the museum of mosaics, the Escola de Canteiros or the centre for the Summer University courses. The monastery is currently devoted to tourist accommodation, governed by the nuns.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.