The apartment is clean and spacious and has everything you would need for a pleasant stay. Beds are comfortable and the 2 bathrooms are very convenient for a group. There are large windows and ceiling windows which let in a lot of light.
The trendy Kreuzberg is a great area with a nice atmosphere, lots of nice coffee shops and restaurants. It´s also within walking distance of 3 subway stops and different U-Bahn lines.
Gregor was a nice host and kind enough to let me in very late in the evening.
I would definitely recommend this place to anyone who visits Berlin and wants to experience more than the city centre.