This triangular fortress with three towers on one side is dedicated to St Olav. It was built in 1475 by the governor of Viborg to protect the eastern provinces of the kingdom. It was extended, and two towers added in the 16-17C - these were razed when the Russians took possession of the site (18C); it also served as a prison for a time. From the towers (30m), there are views of the fabulous landscape of lakes and islands. You can complete your visit at the small castle museum, left of the entrance. To the right, an orthodox museum exhibits precious religious objects.