We had an excellent stay at Matthias' apartment! Everything was as described, the check in/out process very easy. The apartment was very ample for the two of us and could have easily accommodated 1-2 more on the fold out couch. The location is in easy walking distance to many sites - Natural History Museum, Brandenburg Gate, the Reichstag, and the River Spree - and easy access to the U6 line. If we are in Berlin again, this apartment will be our first choice and is much nicer than staying in a hotel.