The Monastery of San Pedro de Villanueva is a Romanesque monastery previously owned by the order of Benedictines. A church here supposedly was founded by Alfonso I the Catholic, son in law of Pelagius of Asturias. The remaining structures now date from later periods. In the 12th century, the monastery was built adjacent to the church. The buildings underwent substantial rebuilding after the 17th century. In 1835, the monastery was dissolved. In the present century, the monastery has become a national hotel, a Parador. The church is still in use.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.