Hachenburg Castle, former seat of the Counts of Sayn, was founded about 1180 by Count Heinrich II of Sayn. Building was finished in 1212 under Count Heinrich III, the founder's son, who was also mentioned as the town's and the castle's first owner. The castle church only arose in the late 15th century and underwent several remodellings until the 18th century.
In 13 October 1654, there was a great fire which burned down the inner town and also the castle. Counts Salentin von Manderscheid and Georg Friedrich von Sayn-Hachenburg undertook to build the town anew, and also the castle, although this time as a Baroque structure. The sweeping Baroque castle was built to architect Julius Ludwig Rothweil's plans between 1715 and 1746. It has had many owners over the last century. For a few decades, however, it has been the seat of Deutsche Bundesbank’s training centre and professional college.
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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.