My family and I stayed in Katarina's apartment while we were in Berlin for the marathon. The apartment is very centrally located. We walked to all of the major sites, and took one of the many metro lines to attractions further out. The apartment itself is spacious, and furnished with all ikea items. It was warm and comfortable enough. Quiet at night. Not a flashy apartment, but in a great location and a good value at the time we were looking. The elevator runs to 6th floor, and then you have to take a flight of stairs to the seventh floor. The check-in office is about a block away from the apartment, so plan accordingly if you're bringing lots of luggage.