The fortified-looking church of Santa María of Baiona, with a Ogival Romanesque style, was built in the 13th century and had the category of collegiate church from 1482 to 1850.
It is divide up in three naves with their respective rectangular apses. The main nave resembles the Cistercian style of Santa María de Oia monastery. Two buttresses flanked the front door in the main façade: three pairs of columns, flat tympanum and archivolts. Windows are Romanesque; there is a marvellous Romanesque rose window up in the main façade. In 1841 several crosses of different styles formerly placed around the village were moved to the portico.
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.