The Church of St. Saviour in Chora, is called Kariye Camii in Turkish, has been converted from a church to a mosque and is now a museum. For me, after Hagia Sophia, it’s the most interesting Byzantine church in the city. Definitely not the the building itself but the superb series of mosaics and frescoes which it preserves and which have been magnificently restored and cleaned. This is one of the best visits for me in İstanbul. The name of the church ‘in Chora’ means in the country because the very ancient monastery to which it was attached was outside the Constantinian walls.
This museum is not that popular with the tourists who have short time to stay in İstanbul. But if you in anyway have an extra half day I would definitely suggest you take a short visit here. Leave yourself to the frescoes and dive into the depths of history. And the great thing here is you can take photographs without flash.