The Mouse Tower is a Gothic octagonal tower from the 14th century, built by King Casimir the Great around 1350. It is the only surviving part of a defensive castle that served a strategic function on the Polish-Teutonic border. In 1657, the castle was destroyed by the Swedes, and the tower survived as a symbol of the city. Currently, it is 32 meters high and is open to visitors, offering a panoramic view of Lake Gopło and the surrounding area. The tower is associated with the legend of King Popiel, who was eaten by mice in the castle tower.