Kruszwica, associated with the beginnings of the Polish state, today is mainly associated with the legend of the evil King Popiel and the Mouse Tower towering over the city. It is a remnant of a 14th-century fortified castle built on the foundation of King Casimir the Great. The castle, once a stronghold on the Polish-Teutonic border, has not survived the test of time, numerous wars and fires. In 1657 it was demolished by the retreating Swedes. Today we can admire the preserved fragments of the walls and the 32 m high octagonal tower. It is worth climbing the 109 winding stairs leading straight to the top. The view from there overlooks the vast waters of Gopło Lake.
Being in Kruszwica, it is worth going to the collegiate church of St. Peter and St. Paul. It is one of the best preserved monuments of Romanesque art in Poland.