Castle of the Masovian Dukes in Ciechanów was built on the turning point of the fourteenth and fifteenth century by Prince Janusz I (1379-1429). The towers located in the four corners of the castle's square formation help to defend the stronghold, and additional 10 metre high defensive walls. Due to dozens of reconstructions and expansions of the castle, the militaristic stronghold transformed into a royal residence. In the fifteenth century, the castle was raised by an additional level and a raised courtyard.
In 1547, the stronghold changed its function into a aristocratic residence. It was the last period of the stronghold's glory. After the Third Partition of Poland, the stronghold became part of Prussia, and was partially deconstructed for cheap building material. In 1818, the castle was owned by the House of Krasiński, in the twentieth century the castle was fully rebuilt.
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.