A small round tower built into the northern stretch of the city wall, distinguished mainly by the dark story attached to it. The tower itself is closed, but you can walk up to the base and read the plaque, then continue along one of the most scenic stretches of the wall walk.
Stories like this — half history, half folk myth — cling to almost every stone in Visby. The locals will tell you a dozen of them if you let them, and the tourist office runs evening walking tours through summer that lean into the gothic atmosphere.