Taivassalo Church is the oldest of the three medieval stone churches in Finland that are dedicated to the Holy Cross. The construction of the church is believed to have begun between the years 1425 to 1440. In 1460s, the third aisle was built and the inner walls were decorated with new murals. It was the first time in Finland that frescos were painted to nearly all important surfaces of a church by a group of professional artists.
The medieval altarpiece as well as wooden sculptures of Taivassalo Church were donated to The National Museum of Finland in 1890. However, Taivassalo Church still has a magnificent triumph crucifix above the altar, in front of the chancel window. This crucifix is one of the oldest and best preserved crucifixes in Finland. The rococo front of the organ, which is unusual by Finnish standards, has remained intact ever since 1767 although the organ has been replaced several times.
As a whole, the church with its murals looks much the same as it would have looked at the end of the Middle Ages.
Ängsö Castle was first named as "Engsev" in a royal charter by king Canute I of Sweden (r. 1167-1196), in which he stated that he had inherited the property after his father Eric IX of Sweden. Until 1272, it was owned by the Riseberga Abbey, and then taken over by Gregers Birgersson.
From 1475 until 1710, it was owned by the Sparre family. The current castle was built as a fortress by riksråd Bengt Fadersson Sparre in the 1480s. In 1522, Ängsö Castle was taken after a siege by king Gustav Vasa, since its owner, Fadersson's son Knut Bengtsson, sided with Christian II of Denmark. However, in 1538 it was given by the king to Bengtsson's daughter Hillevi Knutsdotter, who was married to Arvid Trolle.
In 1710, the castle was taken over by Carl Piper and Christina Piper. Ängsö Castle was owned by the Piper family from 1710 until 1971, and is now owned by the Westmanna foundation. The castle building itself was made into a museum in 1959 and was made a listed building in 1965. It is currently opened to visitors during the summers.
The castle is a cubical building in four stores made by stone and bricks. The lower parts is preserved from the middle ages. It was redecorated and expanded in the 1630s. The 4th storey as well as the roof is from the expansion of Carl Hårleman from 1740-41. It gained its current appearance in the 1740s.