Oulu Castle, built at the mouth of the River Oulujoki in the early 17th century, is part of Oulu’s fascinating history. The city was founded on the mainland opposite the castle. What remains of the castle are some ramparts and the foundation of its stone cellar. The observation tower of the Oulu maritime school, built above the castle cellar in 1875, now houses a summer café. A small exhibition about the history of the castle in its cellar is open to the public during the café’s opening hours.