Tucked behind a high wall in the neighborhood of Fener, St. Mary of the Mongols is a small Byzantine Orthodox church that has been a continuous place of Christian worship prior to the conquest of Istanbul.

Unlike other Byzantine churches in Istanbul, it was never converted into a mosque or a museum. It is said to have once been connected to the Hagia Sophia through a secret underground passageway. 

Today, although it is open to visitors, it is kept under lock and key. The only way in is by ringing the bell next to the door under the sign “Meryem Ana Rum Ortodoks Kilesesi” and waiting for the attendant to let you in. The highlights of this small church are the architecture and intricate icons dating back to the 13th-century.