How to get from Istanbul Airport to the historic center by metro?

Update: the airport metro line to Kadıköy (and connecting ferries) runs 24 hours overnight on Friday-to-Saturday and Saturday-to-Sunday, so you can travel very late at night without worrying about the normal schedule.

Another way to reach the center: take the Havaist bus from the airport to Taksim (Kabataş pier), or the metro with a transfer to Sirkeci (Eminönü pier), then return in the evening by ferry to Kadıköy and take the metro or Havaist back to the airport. Sample timing: leave airport ~20:00, arrive Kadıköy ~21:00, ferry to Eminönü ~21:30, walk around Sultanahmet until ~23:00, take the Tünel funicular to İstiklal and Taksim, walk back past Galata Tower to Karaköy pier by 1am, ferry to Kadıköy ~01:00, taxi to airport around 3am (need to be at the airport by 4am).

Another option via Marmaray from Sirkeci: a new branch line from Halkalı now goes directly to the airport. This works well if your hotel is near the T1 tram line.

Detail on the funicular to Galata Tower: the lower station is in the Karaköy area, just a couple of minutes' walk from Galata Bridge. Get off at the single upper station called 'Beyoğlu', from which it's about 300 meters downhill on foot to the tower.

The return trip to the airport by metro is straightforward: from leaving a hotel in the Aksaray area to entering the airport terminal took 1.5 hours. Signage during line transfers is clear and easy to follow.

Three hours of free time is not enough to visit Galata Tower from the new airport and return without risking a missed flight: allow about 1 hour to exit the airport, at least 1 hour each way in transit, and arrive back at the airport at least 2 hours before departure. Any delay and you will miss your flight.

To reach the Emniyetfaşane area, get off at Ulubaatlı stop rather than Aksaray — it is only a 10–15 minute walk along the main avenue from there, whereas the distance from Aksaray is greater.

From late June, the metro line extends directly to Sultanahmet station, eliminating the need to transfer to the Marmaray. Worth booking a hotel near this station for easy airport access.

Alternative route: metro from the airport to the Kadıköy terminus, then a ferry to Eminönü or Karaköy. Return via Marmaray. Ferries from Kadıköy run from early morning.

Standard route: metro from Istanbul Airport to Ayrılıkçeşme, transfer to Marmaray to Sirkeci. From there you can walk to Hagia Sophia, Blue Mosque, and Basilica Cistern. Allow 2 hours for the round trip, leaving 4–6 hours of sightseeing time (budget 1 hour to exit the airport and 2 hours to return).

From Sirkeci, cross the Galata Bridge, stroll along the Galataport waterfront, then head up to Galata Tower on foot or by funicular, and walk along İstiklal Avenue.

For the Edirnekapı area: start from Eminönü, take bus 32 to Mihrimah Sultan Mosque, then walk downhill through the Chora Monastery (Kariye Mosque) — much easier than climbing up.