This will be my first visit to Berlin, and besides the more obvious things I'd like to visit (Branderburg Gate, Holocaust Memorial, Memorial to Homosexuals Persecuted Under Nazism, Checkpoint Charlie, etc.), I would also like to see less known places and sights. One thing that comes to mind is the art of Walter Womacka, a DDR artist who made magnificent socialist inspired murals, mosaics and even stained glass windows.
I'd love to hear suggestions, what do I have to see in Berlin that's not in your standard tourist book?