Guide de ville
Istanbul: Two Continents, One Connection
New Istanbul Airport opened in 2019 and sits 35km from the city. That sounds far. It's about 45 minutes on the Havaist shuttle. In a city with this much to see, that's nothing.
Transit and visa
Turkey offers e-visa for most western passports (including US and EU). Apply at evisa.gov.tr for around $50 before you leave. It takes minutes. Don't wait until you land.
What's realistic on a long layover
Sultanahmet (the Blue Mosque, Hagia Sophia, the Basilica Cistern) is all within walking distance of each other. A 10-hour layover is enough to see all three and eat well. The Grand Bazaar is worth an hour if you can resist buying everything.
Food that earns the detour
Simit (sesame bread ring) from any street cart, a proper Turkish breakfast at Savoy Pastanesi in Karaköy, or iskender kebap at Kebapçı Iskender. These aren't tourist recommendations. Locals eat here too.