Olvera castle was built in the late 12th century as part of the defensive system of the Emirate of Granada. The castle was seized from the original Moorish builders and occupants and redesigned and expanded under King Alfonso XI in 1327.
Situated at the highest point of the town, the castle has an irregularly-shaped elongated triangle that fits the form of the rock base.
References: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.