Take a boat trip
On a lovely spring afternoon, there is nothing better than hopping on a cruise down the Bosphorus strait, a natural waterway dividing Asian and European sides of Istanbul. Traditional ferryboats depart daily from the Eminönü docks, and take you on a lazy cruise northwards to the Black Sea.
Along the way you'll pass some impressive sights, from the Topkapi Palace and grand Maiden's Tower to the Selimiye Barracks, where Florence Nightingale worked. You'll also stop at several Bosphorous villages – at Anadolu Kavagi there's enough to hop ashore for lunch at one of the fish restaurants.
Go for a walk
Istanbul is an astonishingly beautiful city of narrow ancient streets, dotted with mosques, palaces and sacred springs, spread over seven hills and surrounded on three sides by water. And there is no better way to explore it than on foot.
Start at Karaköy Square and head across the Galata Bridge, which spans the Golden Horn, to Sultanahmet (Old Istanbul), a picture-perfect district where Ottoman minarets crown the skyline.
Most of the city's major monuments are just a few minutes' walk from here, including the opulent Topkapi Palace, the largest and oldest palace in the world.
Make your way to the Egyptian Bazaar (also called the Spice Bazaar), an exotic food market selling everything from spices to Turkish delight.
Visit a café
While café culture in Turkey is not as thriving as, say, in Paris or Vienna, there are some lovely places to stop for a mid-morning cuppa and pastry.
Kaffeehaus, facing Tünel Square, boasts plush blue velvet furnishings and high white ceilings, and is famous for its selection of coffees (and also its resident grey cat).
Grab a table by the window for some unrivalled people watching and order a Turkish kahve, which has the kick of a double espresso.
Equally as lovely is Sedir, located in a converted house next door to the Ortaköy Mosque. It is just like stepping foot into somebody's home, what with its comfy sofas, old books and hand-painted patterns on the walls. The split-level conservatory, with its creeping ivy and stained glass windows, is especially inviting.
Take a look at the Haghia Sophia
If you see only one building while you are in Istanbul, make it the Haghia Sophia ('Divine Wisdom'). After close to 1,000 years as a church and then 500 years as chief mosque of the Ottoman Empire, it is now open as a museum.
One of the greatest surviving examples of Byzantine architecture, its interiors are wonderfully impressive, especially the main chamber, roofed by a fabulous dome, 98ft in diameter. There are some extraordinary mosaics too, the most famous to be found in the galleries on the upper floor.
The Sultanahmet Mosque, known as the Blue Mosque, makes for a great visit too. With its cascade of opulent domes and six slender minarets which pierce the skyline, it is one of the city's most striking images.
Inside is breathtaking too, with chandeliers, blue tiles adorning the walls, intricate stained glass windows and cool floors carpeted with prayer rugs.
Located on the waterfront, Poseidon is one of the most stylish restaurants in the city, serving up superior seafood in a wonderful setting.
It is the perfect place for alfresco dining on a warm evening, with a large deck virtually suspended above the Bosphorus and with sweeping views of Bebek bay. Try a selection of mezze, such as the grilled squid or peppers stuffed with cinnamon rice.
For real Ottoman cuisine book a table at Rumeli in Sultanahmet. A former printworks with a cavernous interior of exposed brick and stained floorboards, it spans several floors, right up to the roof terrace. Expect Ottoman dishes with a Mediterranean twist.