San Colombano Castle originates probably from the 6th century AD, but if was mentioned first time in the 10th century. The current castle was built by Frederick I, Holy Roman Emperor (Federico Barbarossa). During his second visit to Italy, he destroyed the existing castle, but decided to build a new one in 1164. The next reconstruction began in 1370. Later it has been conquered and rebuilt several times.
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.