A strait linking the Black Sea to the Sea of Marmara, which then itself connects to the Mediterranean, the Bosphorus serves as a natural frontier between Europe and Asia.
There are many ferries in Istanbul that sail up the Bosphorus as far as its mouth with the Black Sea, a day excursion you're guaranteed to find enjoyable and relaxing.
As well as being a remarkable channel of water that passes through Istanbul, the Bosphorus is also highly symbolic
in that it represents the geographical boundary between both Europe and Asia and the West and East, and has long been celebrated in in literature and the arts. Around forty kilometers in length and ranging from 600 to 3,000 meters in width, the Bosphorus also constitutes the very heart of Istanbul: a city split in two by the strait, whose banks it occupies on both sides. The Bosphorus is also crossed by two wonderful bridges in the city, and numerous ferries, fishing boats and other types of water craft sail across and up and down its waters.