The apartment is lovely. It is very clean and well thought out. There is everything you could need. It is in a great location,near the U and S- bahn station,and very quiet.Although we never met Bernd and Katja,we were in regular contact,and they were very helpful with directions to the apartment and recommendations for places to eat,shop etc.
I would highly recommend,anyone visiting Berlin, to stay at this apartment. It is great. We will definitely be coming back.