Built around 1420, this is one of the guard towers remaining from the city's once-fortified walls. Crowned by a pointed spire, it was named "witches' tower" because women suspected of witchcraft were locked up here before facing burning at the stake or drowning (their hands and feet were bound, and they were thrown into the river). A collection of instruments of torture from the Middle Ages can be viewed inside. Note: The tower is accessible only via the weekly tour.