Olavinlinna, also known as St. Olaf's Castle, is a 15th-century fortress located on an island in southeastern Finland. Originally built by the Swedes in 1475, this castle has seen its fair share of action over the centuries, withstanding sieges and changing hands multiple times. Today, it's famous for hosting the Savonlinna Opera Festival since 1912, attracting visitors from around the world. With its impressive history and stunning setting, Olavinlinna is a must-visit destination for history buffs and opera lovers alike.