We stayed for five nights at Karsten's studio flat. He greeted us in person and was very helpful. The flat was very well designed, with interesting features, a comfortable bed, and a wonderfully powerful shower. It is light and spacious and in a quiet part of Mitte, so being on the ground floor was not a problem. It's a little out of the way in terms of restaurants,shops and bars, but there is a u-bahn right at the end of the street. We had a couple of good meals in the small German restaurant around the corner. Karsten's other recommendations were good too, and he was really helpful during our stay. Would stay there again if it was available.