Picturesquely set on a river island in the town centre, Kajaani's castle was constructed between 1604 and 1619 to guard the Swedish border from Russia, and destroyed when Russian forces besieged it during the Great Northern War in 1716. The ruins show all the signs of damage by war and time. It’s a fine spot to bask on the grass on a sunny day.
Nearby, a tar-boat channel has a lock built to enable boats laden with tar barrels to pass the Ämmäkoski rapids.