The Pieterskerk (St. Peter's Church) is one of the oldest in Utrecht. Its construction began in 1039 and it was inaugurated on 1 May 1048 by Bernold, Bishop of Utrecht (although the lost west towers were probably only finished about a century after the inauguration). Characteristic of the Romanesque style in which it is built are the church's large nave pillars, each hewn from one piece of red sandstone, and the crypt under the choir. The building is now used by the Walloon Church.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.