Novi Sad
Novi Sad, Serbia’s second-largest city, sits along the banks of the Danube River and has long served as a cultural meeting point in the Balkans. Its centerpiece is Petrovaradin Fortress, a massive 18th-century stronghold nicknamed the "Gibraltar on the Danube." The fortress is known not just for its historic architecture but also for its network of underground tunnels and the iconic clock tower where the hands are reversed, meaning the large hand shows the hour.