The earliest traces of human settlement on the Sulzbach castle hill have been dated to the Late Hallstatt or Early La Tène culture. The medieval settlement was built first in the 8th century or early 9th century. The partially stone-made castle was built there in the 9th or 10th century. In 1003 the castle was moved to the Nordgaugrafen family by Henry II. The medieval castle was rebuilt from 1618 to the Renaissance style. Today the original tower from c. 1100 exists.
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.