This document is prepared for a friend of mine who intend to visit Istanbul. It can be helpful for the other visitors as well...
This is a rail transportation map of Istanbul.
1. Prince Islands (There is a couple of them but I would advice Buyukada.
You can go to Buyukada(Big Island), and take a “fayton” carriage with horses, and take off in Aya Yorgi, after you take off, a step hill is waiting for you to walk. Up there, you can enjoy avery wide view of Istanbul and Marmara sea. There is an old church, for orthodox I suppose, but very important one, people visit in each year in Easter. There is a small, cosy restaurant with nice home made wines.
2. Bosphorus tour
There are a couple of options for that
a. Sehir Hatlari (Big traditional boats, I like them sitting outside the boat. They are not available all time, in the link you can find the schedules.
If you take a long tour, you can leave the boat in Rumelihisari and walk up to the castle for a view of both Karadeniz and Marmara sea.
b. More frequent one but not take you all the up the Bosphorus, upto second bridge.
3. In Sultanahmet there are various museums, but I am sure you do not miss Hagia Sophia (Aya Sofya), Blue Mosque (Sultanahmet) and Topkapi Palace and Harem. But I would also recommend Yerebatan sarnici.
I would suggest you to buy a museum card as well.
4. Galata Bridge, Down the bride there are various fish restaurants, you can try.
5. Grand Bazaar
If you walk to Eminonu from Sultanahmet, you can pass inside the Grandbazaar, which is a must see.
6. Istiklal Caddesi (Taksim), very long straight street, with a tram passing in the middle of the street. It is pedestrian only street; an old one and you can find very interesting things in that area.
a. One is Galata Tower, worth seeing from the top. During the ottoman empire, in 1600s a man called Hazerfen Ahmet Celebi, made an artifical wings and flew through Anatolian part(Uskudar).
b. Nevizade, a small street on Istiklal with many bars, and night life.
c. If you come from Eminonu to Istiklal, you can eat turkish desserts (Baklava) in Karakoy Gulluoglu.
For turkish delights, there are two brands which are very good.
7. Take the boat from Eminonu or Besiktas to Kadikoy. It is in Asian side. The Kadikoy market is very cosy, especially fish market. There are various place to eat something, Kadi Nimet is a place you can eat fresh fishes.
Ciya Restaurant is famous with kebaps and Anatolian cuisine. No reservation is needed for both restaurants.
If you walk in the streets of Kadikoy, you can reach Moda, a very peaceful place for me to have a breakfast with Simit and Cay(tea).
Moda Cay Bahcesi
You can take a taxi from there and you can see the locals best hanging around location in Istanbul, Bagdat Caddesi. (Taxis are not expensive in Turkey, the only concern is the traffic.) you can take off the taxi in Saskinbakkal, which is almost the middle of the very long shopping street.
8. Nisantasi, is one of the luxurious area of Istanbul. With expensive brands and famous faces (Turkish of course). J
Another trendy place is Bebek. I guess it is the best Starbucks view ever in all around the world.
9. From Bebek, you can take a very small boat which is very cheap (5 tl per person) to pass the Anatolian side, Kanlica. It is famous with yogurt, there is a small tea house as well.