Around 1076 Archbishop Gebhard of Salzburg, a follower of Pope Gregory VII in the Investiture Controversy, had the Petersberg fortress erected above the town in order to prevent Emperor Henry IV from crossing the Alps. The archbishop also had fierce enemies in the Carinthian ducal House of Sponheim, who after his deposition made several attempts to take possession of Friesach. Constant attacks by Duke Engelbert were finally repelled in 1124. In 1149 King Conrad III of Germany stayed at the castle on his way back from the Second Crusade, as did Richard the Lionheart returning from the Third Crusade in 1192, attempting to elude the guards of Duke Leopold V of Austria.
Today the castle is home to the Friesach City Museum, which features exhibits about the town's history, culture, mining industry and trade.
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.