Hammershus is the largest medieval fortress complex in Scandinavia — a sprawling ruin of towers, walls, and baileys spread across a granite headland above the sea. It was built in the thirteenth century by the Archbishop of Lund and served as a military stronghold, a prison, and a centre of administration for Bornholm for four centuries.
The fortress was abandoned in 1743 and its stones were subsequently quarried by locals for building material — which is why, rather than a standing castle, you find an atmospheric ruin with walls of varying height and a great deal of interpretive imagination required. What remains is still impressive. The outermost tower commands views across the water to Sweden on clear days, and the path leading up to the gate through rocky heathland gives the approach a suitably ceremonial feel. Entry is free. Allow at least an hour.