Me & my husband went to Istanbul for our honeymoon in April and have to say the place is AMAZING, cant recomend it enough. Must do trips are, the Blue Mosque, Agia Sophia, underground cisterns and a boat trip up the Bosphorus!
We stayed in Sultanhamet which is the old district and has the Grand Bazarr and Spice Bazarr both of which are a must. We also visited a mosque down by the Bosphorus and it was right when they were calling for prayer so we stayed in there for over an hour watching it was the most amazing experience. We visited the Blue Mosque but not the Agia Sophia as the ques were very long and had been warned that its expensive wheras the Blue Mosque is free. The underground cisterns are very worth a visit also. We went over to Taksim Square one night for dinner and then walked down the main high street which is breath taking, so many people so late at night and there is music and lights and a real buzzing atmosphere, the 1940's trams are amazing also.
We walked most places but the tram system is very cheap and very easy to use, we managed to get around very easily, going over from sultanhament to taksim within twenty minutes no problem.
Its pricier in Istanbul than
Icmeler which we were expecting as it is city and you also dont get the same friendliness as in icmeler, i.e. people dont tend to remember you as its such a vast city but the people are still friendly, polite and helpful and we have the most amazing honeymoon there!!
You will love it im sure.