Starý zámok (literally Old Castle) is well preserved castle complex built in the 15th and 16th centuries. It was embedded to the church of Our Lady from the 13th century. The first documented mention dates from 1486. The church was damaged by earthquake in 1443 and the reconstruction to the fortress was made between 1495-1515 against the Turkish threat. The last significant restoration on the defense complex was carried out in 1777.
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.