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:The Gravensteen is a castle in Ghent originating from the Middle Ages. The name means 'castle of the counts' in Dutch. Arnulf I (918–965), Count of Flanders, was the first to fortify this place, building a medieval bastion on this high sand dune, naturally protected by the river Leie and its marshy banks. This bastion consisted of a central wooden building and several surrounding buildings, also in wood.
In the early 11th century, the wooden building was replaced by a stone residence, consisting of three large halls that made up three storeys, connected by a stone stairwell. The monumental stone staircase, the light openings, the fireplaces built into the walls and the latrines were signs of considerable luxury and comfort in those days. There was probably also a tower.