View of the Old Town from the Golden Horn. The is a major urban waterway and the primary inlet of the Bosphorus in Istanbul, Turkey. As a natural estuary that connects with the Bosphorus Strait at the point where the strait meets the Sea of Marmara, the waters of the Golden Horn help define the northern boundary of the peninsula constituting "Old Istanbul" and separates the historic center of Istanbul from the rest of the city, Sulyimaniye Mosque