Eski Imaret Mosque - Credit: Wikimedia Commons
The Eski Imaret Mosque () is a former Byzantine church converted into a mosque by the Ottomans. The church has traditionally been identified as belonging to the Monastery of Christ Pantepoptes (), meaning "Christ the all-seeing". It is the only documented 11th-century church in Istanbul which survives intact, and represents a key monument of middle Byzantine architecture. Despite that, it remains among the least studied buildings in the city. Read more on Wikipedia
Source: en.wikipedia.org