Blackbeard's Castle is the name given to a five-storey stone watchtower built by the Danes in 1679, which stands on a hill above Charlotte Amalie overlooking the harbour. The pirate connection is mostly legend — there is no reliable evidence that Edward Teach, known as Blackbeard, ever used the tower — but the story has stuck, and the name is more marketable than "Skytsborg Tower," its original Danish designation.
The tower itself is a compact and well-preserved piece of colonial military architecture. Climbing to the top rewards you with a broad view over the harbour, the town below, and the surrounding islands. The grounds have been developed into a small complex with a pool and a restaurant, and the tower is part of a collection of five National Historic Landmarks in the immediate area, known collectively as the Haagensen Complex — Fort Frederik, the Haagensen House, Government Hill's 99 Steps, and the tower itself.
The 99 Steps leading up the hill from the town below are one of the most photographed features of Charlotte Amalie, a steep and narrow stairway built from ballast bricks brought over in Danish trading ships. They are worth climbing for the view even if you don't continue to the tower.