The Château des ducs de Lorraine (Castle of Dukes of Lorraine or Sierck Castle) may have been a Gallo-Roman fort, but the first historical document of the castle date from 1067. However there is probably nothing left of this first castle. The current castle was built by the archbishop of Trier in the 15th century. French army conquered it in the 17th century and since 1661 it became part of the reign of France. The castle lost its defensive purpose and it was demolished in 1673. Later fortifications was re-enhanced and left to decay several times. In 1866 The Château was acquired by the city of Sierck les Bains.
References: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.