While strolling around Mitte, check out the flagship store of Berlin´s cult women fashion brand. (And try a delicious cinnamon bun at Zeit für Brot next door.)
Osteria Sippi is an incredible simple italian restaurant where everyone feels immediately at home. They not only know their food game but have also an impressive range of really good wines.
Best record store in Berlin. A great selection of Rock, Folk, Indie, Wave, Industrial and especially the huge floor dedicated to House and Techno Records. Staff are typical Berlin-Style - not very friendly but very knowledgeable.
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!