The Kostelec nad Černými lesy Castle is the main landmark of the town. The castle was first documented in 1348. Until 1549, when it was destroyed by fire, the castle served as a hunting lodge of Emperor Ferdinand I. After 1550, it was rebuilt in the Renaissance style. After 1750, baroque modifications were made. Today the castle is owned by Czech University of Life Sciences Prague and is used for social and business purposes. The neighbouring Church of Saint Adalbert is connected with the castle by a covered corridor.
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.