The Mouse Tower (Mäuseturm) is a stone tower on a small island in the Rhine. The Romans were the first to build a structure on this site. It later became part of Franconia, and it fell and had to be rebuilt many times. Hatto II, the Archbishop of Mainz, restored the tower in 968. The story of how it came to be called the 'Mouse Tower' comes from a folk tale (Hatto was being eaten alive by mice in a tower). In 1298 the structure became an official customs collection tower. It was destroyed by a French army in 1689, then rebuilt in 1855 as a Prussian signal tower.
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.