Certainly one of the most interesting and cosmopolitan cities in the world is Istanbul. This is a city of many names and many cultures, both east and west, indeed its residents like to boast that it is the only major city where East meets West, because it sits on two continents.  Be that as it may,  Istanbul=Byzantium=Constantinople is a city of major importance to the history of  Christianity, even though it existed only as a small Roman town in the first century A.D.

Istanbul today is a city of big churches (see Hagia Sophia above) and big mosques, though the churches are mostly museums these days and the Patriarch is not really allowed the freedom to train people for the ministry by having a Christian school or seminary in Istanbul.  But it was not always thus.  This is the city where John Chrysostom preached, and where Constantine helped the church become a legal and licit religion.  This is the city where major church councils have been held, and indeed which was the capital city of all Christianity when Rome was sacked and Byzantine Christianity was on the rise.

The signs are everywhere of the ancient Roman (see aqueducts above) and Christian presence.  And if ancient history is not your thing, the food in this town is also stellar.