There's nothing more revigorating during the dark winter days than spending a couple of hours in a sauna. Germans have mastered the art of sauna and you can find amazing pieces of architecture in the public swimming pools (Stadtbad). I find Stadtbad Neukölln very peculiar in its neoclassic architecture and it's definitely a wallet-friendly option to enjoy some sauna time there. Be prepared to be naked in front of man and woman!
Rixdorf is definitely my favourite area of Berlin, because it is a historic village within in Berlin. At the moment it is under heavy construction, and I found this strange, nearly taken-down building sitting in the middle of the quaint neighbourhood.