Looming over the town is doughty Carlstens Fästning, a fortress constructed in the 1660s after the Swedish takeover of Bohuslän; later building work was completed by convicts sentenced to hard labour. There are smashing archipelago views from the top of its round tower; you can also explore the secret tunnel and in the prison cells learn the story of Lasse Maja, a cross-dressing thief and local Robin Hood figure.
