Sax Castle has Moorish origins (10th–12th century). It was conquered by the Crown of Aragon in 1239 and subsequently ceded to the Crown of Castile under the terms of the Treaty of Almizra. From its position, it dominates the whole city. The keep, whose foundations are laid over a cave, and the bastion tower are the elements that have survived to the present day.
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.