A very good reason to travel West: the C/O, next to the formerly infamous Berliner Zoo tube station, is an awesome museum dedicated to photography and visual media. Previous exhibitions include Larry Clark, Martin Parr, Anton Corbijn, Annie Leibovitz and Stephen Shore.
It is the highest place in Berlin and is made of wartrash. Translated Teufelsberg means "Devils Mountain". The whole area always reminds on how beautiful Berlin is: On one side you see the big city and when you turn around pitch black forrest.
Favorite italian restaurant, great simple food, friendly staff and the coolest atmosphere (vinil music only). Smart to make a reservation before you go.
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!