Istanbul is a city full of muslim and christian culture and traditions.
It´s the only city that is spread on two continents which is also a reason for the cultural influences from Europe and the Orient. It lives from the contrasts of the coexistence and is a great place to visit, full of history and fascinating architecture.
By entering one of those beautiful muslim mosques you will get the same fascinating feeling of being small like in a huge christian church. Those colorful, giant buildings take your breath!
The must sees in Istanbul are, besides numberless other buildings, definitely the Hagia Sofia and next to it the Blue Mosque.