Bosphorus is the name of the strait that separates Asia and Europe. It looks like a wide river flowing from the Black Sea to the Marmara Sea. It is fairly recent, dating to about 5600 BC. With new discoveries of Neolithic settlements in Istanbul dating back to 6400 BC, we now know that people actually walked from Asia to Europe back then.
Bosphorus is very important for trade and political strategy and has been the target of foreign empires throughout history. The Gallipoli War was an attempt by the British Empire to cross the Çanakkale (Dardanelles) Strait and then control the Bosphorus and Istanbul. After the Ottoman Empire lost the war along with its ally Germany in WWI, British ships invaded the Bosphorus in 1918.
Bosphorus is the most important natural beauty of Istanbul. From Kadıköy on the Marmara Sea in the south to Anadolu Kavağı and Poyrazköy on the Black Sea in the north, the Bosphorus offers visitors a wonderful view of seaside mansions, woods, hills, palaces, and mosques.
There are many ways to do a Bosphorus Cruise for different budgets and durations. A guided tour would be beneficial to not only point out the places of interest but also explain the history behind them.