Of course, go to Istanbul and not brought back the photo of the famous Bosphorus is unforgivable. Here are just places from where you can do it, in the city a great set. If the time is not so much, I advise you to visit Ortaky - a wonderful tourist area with the best view of the famous Istanbul Bridge.
In general, the area is quite old, there is a lot of interesting things nearby (for example, the preserved synagogue, which few people notice). It is nice to take a walk and myself, and with a guide (urban tour, if desired, you can take on Taksim Square, it is not far). The best time to visit, of course, evening. The bridge and the shed at this time are incredibly beautifully highlighted, there is something to see. You can take tea in one of the numerous cafes and enjoy the weather. Be sure to try the local cumper - baked potatoes with different fillings, in Ortak, it is the most delicious.
If you want a shopping, there are very many shops with antique things, but more cautious, a lot of fakes, and the prices are high, especially for tourists. So be careful and bargain! For those who are interested in history there is an Oracle Mosque, one of the symbols of the city. It was not so long ago discovered after restoration, you can appreciate the beauty of Islamic architecture.
In general, the place is very and very colorful, it is nice to spend time to people of any age: and youth (periodically, by the way, exhibitions of street art), and elderly couples, and families with children. The only moment, in the evening the people on the pier are too many, so it is better to come in advance, then good pictures are provided to you.