Yes, you can leave Istanbul Airport (IST) during a layover in 2026, provided you meet two conditions: you have enough time and a valid visa. Because the airport is located about 40–50 km from the city center, you should have a layover of at least 8 to 10 hours to make the trip worthwhile. The M11 Metro line, fully operational in 2026, has significantly cut travel time to the city to about 45–60 minutes. Regarding documentation, many nationalities (including UK, US, and many EU citizens) require an e-Visa or a "Transit Visa" to pass through immigration and enter Turkey. If you are flying with Turkish Airlines, they offer a free "Touristanbul" service for layovers between 6 and 24 hours, which includes transportation and a guided tour. Just remember that you will have to clear security and passport control again upon your return, so aim to be back at the airport at least 3 hours before your connecting flight in 2026's busy terminal environment.