St. Mary's Church (Mariakyrkan) is the oldest still used building in Sigtuna. The brick-made church was constructed in the mid-13th century and inaugurated in 1247. It was, however, completed probably in 1255, when the archbishop Jarler was buried there. The church was enlarged and sacristy added in the 1280’s. Due the Reformation King Gustav Vasa ordered to demolish the adjacent abbey in 1530 and St. Mary's became a parish church.
The full restoration was made in the 1640’s and the present was added then. Mural paintings were restored between 1904-1905. There are couple medieval artifacts remaining in the church, like fonts, a triumph crucifix and small altarpiece.References:
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.