According to local tradition, the hilltop Coraidelstein castle was founded in 960 by Count Palatine Hermann I. However, the first secure mention of Reichsburg Klotten dates back to 1294. At that time, the castle came under the ownership of the Archbishop of Trier. The transfer to Kurtrier was confirmed in 1346. A knightly family with the same name can be traced back even earlier. From 1410 to 1542, the Lords of Winneburg held the castle as a fief. After that, it underwent division, with Heinrich von Hagen being granted a portion of the castle in 1545. The heirs of Winneburg, the Hausts of Ulmen, the Höins of Hartenfels, as well as Hugo and Gerlach Zandt von Merl, also held shares in the castle. From 1654, Johann Eberhard von Kesselstatt held Burg Klotten as a Kurtrier fief and it remained in the possession of the Reichsfreiherren von Kesselstatt until 1917.
The castle was inhabited until 1830 and at an unspecified time, it fell into ruin.
In 1917, Hans Harney (1877–1954), a former consul and former director of the Deutsche Bank in Düsseldorf, purchased the castle from the Counts of Kesselstatt and had two residential buildings constructed there. In 1952, his daughter Else Harney, along with her partner Wendelin Stahl, established a pottery workshop there. After her death in 1984, Wendelin Stahl continued to operate the workshop there until his own death in 2000, together with his former student Ayca Riedinger.
The oldest part of the castle is the ruin of the Romanesque keep, which cannot be ascended due to a pronounced gap in the masonry. The residential building was constructed in the 16th century and later extended.
The castle is currently privately owned and cannot be visited.
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.