The St.Caherine's Church of Muhu is considered one of the most remarkable early-Gothic buildings in Estonia. It was first mentioned in Hermann von Wartberge's Chronicle dated 1276. The exterior architecture of the Muhu Church is a strict monumental style and its originality is prominent. The Muhu Church has preserved its original shape. Around 1663, a little wooden steeple was added to the church, but perished together with the roof in 1941. In 1993, during the restoration period an additional roof was constructed on the facade of the church to protect the church bell.
As for the interior furnishings of the Muhu Church one will find an altar table made of dolomite, which has been preserved from the time of its original construction. Also the stone base of the baptismal basin originates from the Middle Ages.
The pulpit is in Renaissance style and was completed on 1627. It is one of the oldest in Saaremaa and was made by Balthasar Raschky. The Classicist altar was created by Nommen Lorentzen in 1827. The altar painting has survived from the original altar and the painting was finished in 1788.
In the Muhu Church and churchyard there are worth noting the trapezium-shaped tombstones with pagan symbols found only on the islands and Western Estonia. They have been traced to the 12th and 13th centuries. The most intricate tombstone is presently located in the frame of the door leading to the wall staircase. It is one of the two preserved in Estonia from the 12th-13-th centuries depicting human figures. Through discovering tombstones, bones and some other rare archaelogical finds, the church is thought to have been erected on a sacred site of the ancient Muhu inhabitants.
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.