Kajsar Tower, Visby Ring Wall (Sweden)
Visby is the city in the Gotland Island of the Baltic Sea. It was one of the important centers of the Hanseatic League in the 12th - 14th centuries. The old town is surrounded by a ring wall built in the 13th century. This Kaiser Tower is one of the towers standing on its ring wall. This tower was used as a prison from the end of the 17th century until the early 19th century, and now it is used as the museum.