The peninsula of the Old City was Constantine’s New Rome and Ottoman Stamboul. Here are the key sights: Topkapı Palace, Ayasofia, the Süleymaniye and Blue Mosques, the Covered Bazaar and much else. Take good shoes.
The Old City is quite literally a city within a city. One quarter alone, Fatih, has a million residents, and its Çarşamba Pazarı (Wednesday Market) is the largest street market in the world. Sultanahmet, at the tip of the peninsula, is the starting point for any visitor, but Istanbul’s greatest architecture is spread across the seven hills. The Old City is also a living, lively place, where ferryboats still carry commuters in their hundreds of thousands to work every day. The grit of its bazaars is all part of its charm.
The unmissable gems are three Byzantine monuments: Ayasofya, the Church of the Chora (Kariye Camii) and the land walls; and four Ottoman: Topkapı Palace with its deceptively plain courtyards, the bazaars (grand and spice and everything between), Süleyman the Magnificent’s Süleymaniye and the 16th-century mosques of his grand viziers Rüstem Pasha (in the Spice Bazaar) and Sokullu Mehmet Pasha behind the Sultan Ahmet complex. Byzantinists will add the Fethiye Camii (the Pammakoristos church) on their way to the Kariye, and Ottomanists the nearby Yavuz Selim.