Kärnan — the name means "the keep" — is the squat medieval tower that gives Helsingborg its skyline. It is all that remains of a vast fortress that once controlled the narrowest crossing of the Øresund: whoever held this tower collected tolls from every ship passing between the North Sea and the Baltic. The tower changed hands between Denmark and Sweden more than once before Sweden finally took permanent control in 1658.
The climb to the top earns the best view in the city: on a clear day you can see individual buildings in Helsingør across the water, and on the clearest days, Copenhagen's spires further south. Inside, the rooms have been restored to show how the medieval garrison lived, with exhibitions on the fortress history at each level.