Yeah, Savonlinna is a city. I'm actually pretty surprised, I thought Tuomiokirkko would've been the one.
Well, it says here: "The Castle of Olavinlinna was constructed in 1475. This magnificent castle, has its strategic position along the canal that connects the numerous lakes of Finland. The castle defended the border against Russia.
Due to the summer operas, this castle has become, more than ever, a meeting point between East and West.*"
*)With the cooperation of Finland
I guess that's why they created this castle instead of the Tuomiokirko.