The apartment is beautiful and very light and bright and spacious. It overlooks a green courtyard which is very quiet most of the time.
Communication is excellent and for the most part the apartment was very quiet except my last morning when the downstairs neighbors were playing deep-bass trance music starting at 7:00am!
It's super close to transportation and the cafe on the corner has delicious salads. The neighborhood seems safe for walking at night and it's close to lots of neighborhood cafes and restaurants.
I loved the apartment, the owners, and Berlin. This is a great place to stay if you don't mind carrying your luggage by hand up 74 stairs. I mean it's doable, but best to prepare yourself mentally beforehand.
Stay at Luke and Claudia's place and enjoy Berlin.