The oldest parts of Gerum Church are the choir and apse, dating from circa 1200 and Romanesque in style. The presently visible, Gothic nave dates from a later time of the 13th century and probably replaced an earlier, Romanesque nave. The tower, which was never finished, was built circa 1300. The only non-medieval part of the church is the sacristy, built in 1835.
Gerum Church is constructed of limestone. The exterior is whitewashed apart from several finely carved stone details. The façade is broken by four windows on the southern side while the northern completely lacks windows. The church has three portals, one Romanesque in the choir and two Gothic in the nave and tower, respectively. The Gothic portals are decorated with stone sculptures. Inside, the church carries frescos from at least three different periods: the 13th century, the 15th century (by the Master of the Passion of Christ) and the 18th century. The church also has a decorated stained glass window from the 14th century.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.