The fortress in Muiden, known as Muizenfort is part of the Stelling van Amsterdam, the UNESCO World Heritage site that consists of a set of forts around the city of Amsterdam. The defence line was 135 km long ring of fortifications around Amsterdam, consisting of 42 forts located between 10 to 15 kilometers the centre, and lowlands that can easily be flooded in time of war. The flooding was designed to give a depth of about 30 cm, insufficient for boats to traverse. Any buildings within 1 km of the line had to be made of wood, so that they could be burnt and the obstruction removed. The Stelling van Amsterdam was constructed between 1880 and 1920. The invention of the aeroplane and tankmade the forts obsolete almost as soon as they were finished.
These days, the Muiden fort is used for offices as well as a small museum, the Muider Muizenfort Museum (MMM).
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.