Built originally in 1308, it helped protect old Christiania from pirates and marauders throughout the periods of Danish and Swedish dominance. Stone paths through the grounds of the fortress lead to crenellated walls that open to the town below. It's an impressive view. Moored at the docks below the walls are some of the oldest wooden sailing vessels still in use in the world. One magnificent schooner dates back to 1854.
Most vessels are open for charter.
West of the harbor is the Bygdoy peninsula, where the old Viking ships and other Norwegian sailing crafts are kept. Explorer Thor Heyerdahl's famous Kon Tiki is on display here. It's the famous balsa-wood raft that in 1947 floated across the Pacific hoping to prove the theory that the Polynesian islanders originated from South America and migrated to the Pacific. There is also on display the Egyptian reed boat Ra that Heyerdahl used on a later expedition. Boating enthusiasts will love Oslo.