Istanbul

The single most astonishing building in Istanbul, and arguably the most consequential in the history of architecture. Emperor Justinian raised it as a cathedral in 537, its dome so wide and shallow that for a thousand years nothing rivalled it; the Ottomans made it a mosque in 1453 and added the minarets, and after decades as a museum it returned to working-mosque status in 2020. It remains a UNESCO World Heritage Site. Inside, the sheer scale stops people mid-step, and the surviving gold Byzantine mosaics of Christ, the Virgin and the emperors glimmer high on the walls above Islamic calligraphic roundels, a rare overlay of two faiths in one space. Tourists now enter through the upper gallery, where the best mosaics and the famous dome views are found. Come at opening to beat both the crowds and the heat, dress modestly, and steer well clear of Friday midday prayers.

Facing Hagia Sophia across a garden of fountains and rose beds, Sultan Ahmed I's early-seventeenth-century mosque is the more graceful of the pair, and it is still very much a living place of worship with free entry. Its popular name comes from the more than twenty thousand hand-painted Iznik tiles, tulips, carnations and cypresses in blues and greens, that line the upper walls and catch the light from around two hundred and sixty windows. Six slender minarets set it apart; the story goes that the sultan asked for gold (altın) minarets and his architect heard six (altı). A recent multi-year restoration has left the vast prayer hall looking its best in generations. Enter through the courtyard, remove your shoes, dress modestly, and time your visit between the five daily prayers. The interior is free, unhurried and genuinely moving, one of the city's few unmissable sights that costs nothing.

For almost four centuries this was the nerve centre of the Ottoman Empire, a walled city of courtyards, pavilions and gardens on the point where the Bosphorus meets the Golden Horn. It is less a single palace than a sequence of them, so plan a good half-day. The Imperial Treasury dazzles with the emerald-studded Topkapi dagger and the 86-carat Spoonmaker's Diamond, while the Chamber of Sacred Relics holds objects associated with the Prophet Muhammad, viewed with appropriate reverence. The separately ticketed Harem, a warren of tiled private apartments where the sultan's family and household lived, is worth every extra lira. Don't rush the fourth courtyard, whose terraces and tulip gardens offer some of the finest Bosphorus views in the city. Arrive right at opening to stay ahead of the tour groups, and note that the palace closes on Tuesdays. Comfortable shoes matter here more than almost anywhere else.

One of the oldest and largest covered markets on the planet, a roofed labyrinth of more than sixty streets and thousands of shops that has traded continuously since the fifteenth century. Under its painted vaults you find carpets and kilims, gold and silver, ceramics and Iznik-style tiles, lanterns, leather, textiles and Turkish delight, loosely grouped by trade so the goldsmiths cluster in one lane and the carpet dealers in another. Bargaining is not just accepted but expected: start well below the asking price, stay good-humoured, and be ready to walk away, which often produces the real price. Even if you buy nothing, the architecture, the hans (old merchant courtyards) tucked off the main lanes, and the endless glasses of offered tea make it worth an hour or two. Go on a weekday morning when it is calmer, keep your bag zipped in the crush, and remember it closes on Sundays.

Hidden beneath the streets a short walk from Hagia Sophia lies the largest of the Byzantine cisterns that once stored water for the imperial city, built under Justinian in the sixth century. Descending the stairway into the cool, cathedral-like dark is a genuine surprise in the middle of a hot day: 336 marble columns, many salvaged from older Roman buildings, march away in rows over a shallow sheet of water patrolled by carp. At the far corner sit the two celebrated Medusa heads used as column bases, one upside down and one on its side, their origin still a mystery. A recent restoration added dramatic lighting, sculpture and raised walkways, so it now feels part monument, part art installation. It is compact, atmospheric and blissfully cool. Come first thing to avoid the queues that build by late morning, and mind the damp, uneven footing underfoot.

No visit is complete without getting out onto the strait that splits the city and two continents. From the water, Istanbul rearranges itself into a single sweeping panorama: Ottoman waterfront mansions (yalıs), the fairy-tale Dolmabahçe and Çırağan palaces, the fortress of Rumeli Hisarı, and the great suspension bridges linking Europe to Asia. You have two easy choices. The cheapest and most local is the scheduled public ferry, especially the long Bosphorus tour boats from Eminönü, where a few lira buys the same views the tour boats charge much more for. Private and small-group cruises, some at sunset with dinner, add commentary and comfort. Either way, sit on the right-hand side heading north for the palace-lined European shore, bring a light layer as it is breezy on deck, and time it for late afternoon when the low sun turns the domes and water to gold. Ferries also make a perfect cheap crossing to Asian Kadıköy.