Molla Zeyrek Mosque

Zeyrek Mosque or the Monastery of the Pantokrator, is a large mosque on the Fazilet Street in the Zeyrek district of Fatih in Istanbul, overlooking the Golden Horn. It is made up of two former Byzantine churches and a chapel joined together and represents the best example of Middle Byzantine architecture in Constantinople. After Hagia Sophia, it is the largest Byzantine religious edifice still standing in Istanbul.

It is less than 1 km to the southeast of Eski Imaret Mosque, another Byzantine church that was turned into a mosque.

Source: Wikipedia