Istanbul is more than one city
Byzantium, Konstantinople, Istanbul has always been a city of many different cultures and now more than ever it is almost like several cities all thrown together, you can have a taste of the world just a 1 euro tram, metro or ferry trip away. I only spent 8 days in this city but tried tasting a little of each area. Dig underneath for Byzantine remains. See Galata for artistic culture of hipster bars and cafes, or the Asian side for a European metropolis feel. Islands and palaces. There is a lot!
Insider Tip:I found it relatively safe, although I travelled in winter, but I did run into a few little scammers but nothing serious, just watch out for the mobile shoe shiners who conveniently "drop" their brushes right in front of you. Only happened sat and Sundays for me, or an "overly friendly and inquisitive local".. If you love history there are a few places you can climb up the top of the great walls along the old golden gate, for a beautiful view of the entire city, old and new and across the straits!