Please note, Ataturk Airport closed in 2019. Istanbul Airport (IST) operates on the European side, while Sabiha Gökçen Airport (SAW) is located on the Asian side of Istanbul.
You can go from Istanbul's Atatürk Airport, on the European side of Istanbul, to Sabiha Gökçen Airport, 60 km (37 miles) to the east on the Asian side of the Bosphorus (or vice-versa) by public transport in about two hours, and see a good amount of Istanbul and the Bosphorus as you travel. Here's how:
Airport Buses via Taksim Square
There is no non-stop airport bus service between Istanbul's two airports, but you can make the trip by changing buses at Taksim Square.
Havabüs operates airport buses between Atatürk Airportand Taksim Square (TL12), and Sabiha Gökçen Airportand Taksim Square (TL15; thus, total fare for the journey TL27). Though the airport to airport trip takes 2 to 2-1/2 hours in light to normal traffic, you should allow more time at heavy-traffic times.
Efendi Travel will drive you from one Istanbul airport to the other in a comfortable Mercedes-Benz or other quality minivan for not all that much more than a regular Istanbul taxi, but the ride is far more pleasant, assured and safe. It's the fastest way to go, taking about 1-1/4 hours in normal traffic (up to 2.5 hours during the afternoon and evening weekday traffic rush, 15:00 [3 pm] to 21:00 [9 pm]).
The total fare for the van is 55 euros, and it can take up to four passengers and their luggage, so if you're traveling with three others, the fare will be not much more per person than the fares for the airport bus, but faster, more comfortable and more convenient, without the need to change airport buses (unloading, waiting, then re-loading your luggage) at Taksim Square.
Your private transfer begins in the airport terminal at the Customs-area exit where you will be met by an Efendi Travelstaff person holding a sign with your name on it, who will assist you with your luggage. A professional driver will take you across the Bosphorus to the other airport offering snacks and beverages along the way, and will help with your luggage when you reach the other airport. The cost is the same for one to four persons—it's not a per-person charge. This is a great value-for-money service. More...
There are usually Istanbul taxis waiting at the airport to take up to three passengers with light luggage to the city center or the other airport. Most of the time the trip is uneventful. Sometimes the driver tries to charge more than the standard fare, or takes "the long way round."
Occasionally the driver will want to stop and usher you into a carpet or leather apparel shop from which he earns a commission. More...
In a few years Istanbul's M4 Metro line will come even closer to Sabiha Gökçen Airport, to Pendik and the ferryboat docks at Kaynarca, but for now, here are the links in your journey between Atatürk Airport and Sabiha Gökçen Airport by Metro and Marmaray:
Marmaray: Yenikapı to Ayrılık Çeşmesi
M4 Metro: Ayrılık Çeşmesi to Kartal
E10, KM20 or KM22 Bus: Kartal Metro to Sabiha Gökçen Airport
This journey may take several hours: waiting for the bus, walking to and from Metro and Marmaray stations, long walks within some stations, etc., but it is the cheapest way. With an Istanbulkart it should cost less than TL8. Full-fare using tokens would be TL16.
—by Tom Brosnahan