Istanbul is where Europe meets Asia, where Byzantine mosaics share walls with Ottoman calligraphy, and where a fisherman grilling mackerel on a bridge can be your best meal of the day. The city has been a capital of three empires, and that layered history makes every neighborhood a discovery.
The best time to visit is April through May or September through November. Spring brings tulip festivals and mild weather. Autumn has warm days and thinner crowds. Summer can be very hot (above 35 degrees Celsius) with heavy tourism. Winter is cold and rainy but atmospheric, especially with snow on the mosques.
Sultanahmet is where the headline attractions sit — Hagia Sophia, the Blue Mosque, Topkapi Palace, and the Basilica Cistern are all within walking distance. The Grand Bazaar and Spice Bazaar are nearby. Cross the Galata Bridge to Beyoglu for Istiklal Avenue, the city's main shopping and nightlife strip. Kadikoy on the Asian side is a foodie destination with a vibrant market and excellent meyhanes (Turkish taverns).
Practical tips: get an Istanbulkart for all public transit including ferries. Take the ferry to the Asian side — it costs almost nothing and the Bosphorus views are spectacular. Turkish breakfast (kahvalti) is an event — order a full spread and plan to spend two hours. Tipping 10 percent is standard at restaurants. The call to prayer echoes across the city five times a day — it is one of the most atmospheric sounds you will hear anywhere.