I had a great stay at Claudia and Steffen's concrete apartment. The key was very easy to find and everything was relaxed and self explanatory.
The room looks exactly as in the pictures and is very comfortable and clean.
The view over Berlin and into the "concrete sky" is extraordinary and fun to wake up to and go to bed to.
The building is situated in the center of the Berlin MITTE and 2 minutes away form the Hackesche Markt. The many Ubahn, Sbahn and Strassenbahn as well as bus connections make this a perfect starting point to all the Berlin attractions. For a tourist thee might not be a much better location in Berlin.