Niederkastenholz castle is surrounded by a moat, with an angular main castle and a separate horse-shoe shaped fore-castle with working quarters. It used to belong to Kornelimünster Abbey. The rough stone buildings of the castle are complemented by the wrought-iron gate. The fortified tower dates back to the 12th century and is the oldest part of the castle.
The so-called Probstei was added onto the medieval main castle between 1752 and 1756. Part of the moat is still visible today, although most of it was filled in during the 19th century.
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Visby Cathedral (also known as St. Mary’s Church) is the only survived medieval church in Visby. It was originally built for German merchants and inaugurated in 1225. Around the year 1350 the church was enlarged and converted into a basilica. The two-storey magazine was also added then above the nave as a warehouse for merchants.
Following the Reformation, the church was transformed into a parish church for the town of Visby. All other churches were abandoned. Shortly after the Reformation, in 1572, Gotland was made into its own Diocese, and the church designated its cathedral.
There is not much left of the original interior. The font is made of local red marble in the 13th century. The pulpit was made in Lübeck in 1684. There are 400 graves under the church floor.