Central and friendly apartment, just a few meters away from the famous Taksim-square. The apartment was clean and Isik also provided a large bottle of drinking water which was very practical. The only negative point is that there was a lot of noise from the street and from planes overflying the rooftop apartment but of course it's difficult to find a quite and a central apartment. Directly on the Taksim-square there is a metro-station and Isik also left an (empty) Istanbul-card with which you can travel around the city more cheaply than if you buy a ticket for each trip.
A friend of Isik came to the bus-station near Taksim at midnight in order to welcome me and showed me the way to the apartment.
I recommand it. Thank you Isik!