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!
I often go exploring into random and dilapidated areas of Berlin. I like the thrill of finding new nooks and crannies with strange visual sites. A few months ago, an old housing colony was abandoned, and many objects (such as couches and front doors) were left at the edge of the city to rot or to be scavenged. This is a view from a non-descript area of the S-bahn train tracks (between Sonnennallee station and Treptower Park station) into the most Southern part of Neukölln district.
New type of museum. It's a private collection from contemporary art pieces such as by Anish Kapoor or Nobuyoshi Araki to Chinese imperial furnitures or ancient Asian sculptures. The collection is wonderful and the light design is perfect. There is no description or title of the artworks - it invites you to purely see/feel the artworks themselves without influencing by the names. Must to go.
Haus der Materialisierung is an association of various local initiatives and institutions that research, practice, and work on the topics of sustainable management and climate-friendly use of resources.
...and it works!