Petra and Ottos apartment is brilliant for a stay in Berlin. It's clean and spacious. We were 4 friends staying in the apartment and there was sufficient space. The apartment is located in an very nice neighborhood. It's very quiet and you will find 2-3 groceries within 200 meters. The tram is very close as well and you can walk the 2 kilometres to Alexanderplatz. Otto is easy to communicate with. Otto welcomed us at the apartment even though it was in the middle of the night. I can fully recommend this apartment.