I can only echo what other guests have said, Metin was an excellent host for our 5 night stay, and very helpful in advice on the City attractions and things like arranging an airport transfer as we were nervous arriving in a new City after dark.
The appartment and the location is as described - a historic building on Soguk Cesme street - part of the walls around the Topkapi Palace - so central that the entrance to Gulhane Park with its Archaeological Museum is at one end of the street, and Hagia Sophia further up the slope. The 'Blue Mosque' is no more than 5 minutes walk, whilst trams (to the metro/Airport connections or to Galata) and the main rail station and ferry routes (for Marmary/crossing to Asia side) are also extremely close.
The area is served by abundant restaurants and cafe's and we were able to experience the sights and sounds of the historic centre of Old Istanbul at our leisure, without needing to worry about long journeys to and from our accomodation.
There was a little noise from the cafe outside the appartment, but certainly not enough to trouble us after many full days exploring the City we slept soundly each night!
My daughter and I would certainly go back and Metin's ayasofya house would be our first choice location!