Where is the Bosphorus?

The Bosphorus is about 31 km long and, at its narrowest, only around 700 metres wide. It forms part of the boundary between Europe and Asia, splitting Istanbul into European and Asian sides. Together with the Dardanelles and the Sea of Marmara, it is the only sea route between the Black Sea and the Mediterranean, making it one of the busiest and most strategic waterways in the world. Three suspension bridges now cross it, along with the Marmaray rail tunnel opened in 2013 and the Eurasia road tunnel opened in 2016. Its waters have two layers of current, with fresher water flowing south on top and saltier water flowing north below.