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.

You can see more of the region where this and several others is situated on my Istanbul Seventh Hill gallery.