Cronk Howe Mooar is a motte and bailey castle from the late 11th or early 12th century. Steep sided, flat topped and grass covered, 30 to 35 feet high, diameter about 140 feet, surrounded by a well marked ditch which, on the east, cuts across a low spur projecting in that direction. There are faint traces of earthbanks in the wet ground east of the mound.
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.