Bosphorus is a strait that forms part of the boundary between the European part of
Turkey (Thrace) and its Asian part (Anatolia). It is one of the Turkish Straits, along with the Dardanelles. The world's narrowest strait used for international navigation, it connects the Black Sea with the Sea of Marmara (which is connected by the Dardanelles to the Aegean Sea, and thereby to the Mediterranean Sea). It is approximately 30 km (19 mi) long, with a maximum width of 3,700 m (12,139 ft) at the northern entrance, and a minimum width of 700 m (2,297 ft) between Kandilli and Aşiyan; and 750 m (2,461 ft) between Anadoluhisarı and Rumelihisarı. The depth varies from 36 to 124 m (118 to 407 ft) in midstream. The shores of the strait are heavily populated as the city of
Two bridges cross the Bosporus. The first, the Bosphorus Bridge, is 1,074 m (3,524 ft) long and was completed in 1973. The second, Fatih Sultan Mehmet (Bosphorus II) Bridge, is 1,090 m (3,576 ft) long, and was completed in 1988 about 5 km (3 mi) north of the first bridge. Plans for a third road bridge, which will allow transit traffic to by-pass the city traffic, have been approved by the Ministry of Transportation. The bridge will be part of the "Northern Marmara Motorway", which will be further integrated with the existing Black Sea Coastal Highway. The location will be somewhere north of the existing two bridges, but the exact path is kept secret to prevent false rumour trading of lands on the possible routes. Another crossing, Marmaray, is a 13.7 km (8.5 mi) long undersea railway tunnel currently under construction and is expected to be completed in 2012. Approximately 1,400 m (4,593 ft) of the tunnel will run under the strait, at a depth of about 55 m (180 ft).
A cheap way to explore the Bosporus is offered by the public ferries that traverse the Bosporus from Emin�n� on the historic peninsula of Istanbul to Anadolu Kavağı near the Black Sea, zigzagging between the Rumelian and Anatolian sides of the city. It is also possible to experience the Bosphorus by taking a regular ride in one of the public ferries that travel every 45 minutes between the European and the Asian sides. It is also possible to travel by the privately owned ferries available between �sk�dar and Beşiktaş. There are also tourist rides available in various places along the coasts of the Bosphorus. The prices vary according to the type of the ride, and some feature loud popular music for the duration of the trip .