We had a great time in Istanbul! Osman picked us up at Taksim Square (easy to reach with a direct bus from the airport), showed us his nice apartment and gave us good recommendations for sightseeing, food etc. In particular a breakfast place very close the apartment is great, try it! The old part of Istanbul (Hagia Sophia etc.) is just a few tram stops away, and for the evening/night you have everything you want in walking distance.