The modern subway and tram system is one of the most convenient means of transportation in Istanbul.
To get on a metro, tram or funicular you have to pass the turnstiles in order to reach the platform. To pass the turnstiles, you either need to buy a token (jeton) or use your pre-loaded akbil (electronic travel pass) or İstanbulkart, a contactless electronic card similar to the ones used in London (Oyster) and Paris (Navigo).
The Istanbulkart is sold at ticket booths near major transportation hubs like Eminönü, Taksim and Beşiktaş. Also it’s widely available at the newspaper stands and kiosks near major transit stops such as Eminönü, Sultanahmet, Sirkeci, Taksim, etc.
You pay a deposit of 10 lira for the card itself (which is refundable when you’ll return the card), then you can load as much credit as you’d like on it using the self-service kiosks named as (ISTANBULKART DOLUM NOKTASI, meaning 'Istanbulkart refill point').
You can use your Istanbulkart for more than one person. It provides discounts for both each independent ride and every connecting ride within two hours.
Please Note: Istanbulkarts are not sold at Atatürk Airport.
Two lines of Istanbul's Metro system are in operation. Metro stations are marked with letter M in blue and red colors.
The Istanbul Metro, or the M2 (The Şişhane-Atatürk Oto Sanayii Metro Line), is a mass transit underground railway network, running from the Atatürk Oto Sanayi station at Maslak in the north to the Sishane station at Beyoglu in the south.
The tram lines are Zeytinburnu-Kabatas, Gungoren-Bagcilar and Edirnekapi-Sultanciftligi. Taksim, the cultural and entertainment centre of the city is accessible from Kabatas by a short funicular railway.
There are two funiculars in Istanbul. One is called as TÜNEL (F-2) which is one of the oldest subways of the world dated back to the Ottoman Empire. Tünel climbs the hill from Karaköy to Beyoğlu (Istiklal Street). There there is a connection possible with the nostalgic tram (T-5) that goes all way to the famous Taksim Square.
The other funicular (F-1) is more modern in design and climbs the hill from Kabataş to Taksim (it has a seemless connection with the T-1 tram line and M-2 metro line).
LIGHT RAIL SYSTEM:
A light rail line, known as M1, runs from Yusufpasa, near Aksaray, to Esenler and Atatürk Airport.
The most useful for visitors is the light-rail line connecting Atatürk Airport and Aksaray Square via Istanbul's mammoth Otogar (intercity bus station), at which you can board a bus to any part of Turkey or to virtually any country within 1,000 miles (1,600 km) of Istanbul. Change from the Metro to the tram at Zeytinburnu to reach Old Istanbul and Sultanahmet Square.
Trains departing from Sirkeci and Haydarpasa reach the outer parts of the city.