Istanbul is one of the world's most unique cities because it is the only major metropolis that spans two continents: Europe and Asia. The city is split by the Bosphorus Strait, a narrow waterway that connects the Black Sea with the Sea of Marmara. The western half of the city lies on the European side, while the eastern half lies on the Asian side. Istanbul has served as the capital of three major empires (Roman, Byzantine, and Ottoman) and its transcontinental status has made it a bridge between Eastern and Western cultures for centuries. You can literally cross from Europe to Asia in a matter of minutes via a ferry or over one of the three Bosphorus bridges.