This is the Church of The Holy Saviour in Chora. It’s a famous church for its mosaics and frescoes. The Chora Church is considered to be one of the most beautiful surviving example of a Byzantine church.
The original of this church was built in the early 5th century. However, it was only after the third phase of building, in the 14th century, that the church as it stands today was completed. And around fifty years after the fall of Canstinople (1453), the church was converted into a mosque. Now and since 1958, it was opened to public as a museum.
Here’s some photos of the frescoes :
And the mosaics :