St. Nicolai Church dates to the 13th century. Originally built in late Romanesque style and dedicated to the patron saint of merchants and seafarers, the church is the oldest building in the community. Renovations in the 15th century developed the church into a Gothic hall with two transepts and a tower 27.2 m high.
On display in a glass-covered sarcophagus in the northern transept are the remains of the Haraldskær Woman, one of the best conserved of the iron age bog bodies. The southern transept houses the sarcophagi of Kai de la Mare and his wife. The exterior brick wall of the north transept has an interesting feature of 23 spherical indentations approximately 15 cm in diameter, which hold the skulls of 23 robbers who were caught and beheaded in the nearby Nørreskov forest. In front of the church stands a sculpture of the priest Anders Sørensen Vedel.
The church was seriously damaged during the Thirty Years' War by the Catholic troops of Wallenstein. Since that time it has undergone several major restorations: in 1744, 1855-56, 1887-88 and 1964-66.
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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.