We had a great time at Onur's place. The apartment is spacious, clean and well-equipped, and it is located in such a lovely historic district that we enjoyed exploring. The balcony is certainly a highlight: it's huge, very comfortable (the swing was everyone's favorite) and provides an amazing view of Bosphorus. We have literally spent a whole day just sitting there and watching the ships passing by.
One notable downside is the lack of air conditioning, some sunny summer mornings were really hot, and opening windows didn't help much. Also note that there's no elevator in the building, and climbing stairs to the 6th floor might not work for some older folks.