This is the Koca Mustafa Paşa complex. It's mosque is a former church, St. Andrew in Krisei. Inside are some good capitals, the light was too low to take their picture.Nearby is the shrine of the famous Istanbul folk-saint Sümbül Efendi, who was the first sheik of the dervish tekke which was established here in the 16th century.

Inside the mosque, you can see it started as a church.