I had a very pleasant extended stay (five weeks) at Martha's place in Pankow. The flat is comfortable and spacious, and very quiet, as it faces a courtyard rather than the street. Nice big windows and a cute little garden that one has access to. The place is well stocked with kitchen utensils, bedding, etc. - everything one would need. It's a short walk to the Pankow U- and S-bahn stop and there are several great supermarkets nearby, as well as a couple of nice coffee shops. Martha was prompt and friendly in her communication; check in and check out were smooth. I'd definitely stay there again.