Istanbul sits on a strait, and the strait is why the city exists. The Bosphorus runs about thirty kilometres from the Sea of Marmara to the Black Sea, and it is a working waterway: tankers, commuter ferries, fishing boats and tour boats share one channel. Cruises here split into three kinds. Public ferries from Eminönü run a long route up to Anadolu Kavağı near the Black Sea mouth, with a stop of about two hours, and a shorter circular tour of roughly ninety minutes. Private boats leave from Eminönü, Kabataş, Karaköy and Ortaköy. Dinner cruises add music and a set menu.

What you see from the water is the side of Istanbul built to be seen from it. Dolmabahçe Palace stretches along the European shore; Ortaköy Mosque stands directly beneath the 1973 bridge; Rumeli Hisarı, the fortress Mehmed II raised in 1452 to cut the city off from Black Sea supply, still holds the narrowest point. Beylerbeyi Palace faces it from the Asian side, and between them run the wooden yalı mansions that were summer houses for Ottoman families. The Maiden's Tower sits on its own islet off Üsküdar. A separate line goes up the Golden Horn to Eyüp, and ferries to the Princes' Islands take about an hour and a half, where private cars are not allowed.

Practical: public ferries are paid with an Istanbulkart and cost a fraction of a tour boat, but they run to a timetable and nobody narrates. On the long route, check the return departure before stepping off at Anadolu Kavağı. Sunset slots on private boats go first. The deck is windy even in July, so bring a layer, and the strait turns choppy when the north wind sets in. Ask whether hotel transfer is included and whether the boat has an open upper deck, because the same route seen through a closed cabin window is worth much less.