Vardøhus Fortress is the world's northernmost star fort — an eight-pointed bastion fortification built by order of King Christian VI of Denmark-Norway in 1738, on the site of an earlier medieval fortification that guarded Norway's Arctic frontier. The fort is still technically an active military installation, garrisoned by a small Norwegian Army unit, which makes it a working piece of history in a way that most Scandinavian historic monuments are not.
The star-shaped earthwork ramparts and the central keep are open to visitors during summer. You can walk the full circuit of the bastions, inspect the old cannons, and visit the small museum inside the keep. The view from the ramparts across the harbour and out to the open Barents Sea is worth the short walk from the town centre. The fortress is a ten-minute walk west of the main square.