Orchidea: It's really small, therefore you might have to wait for a table. Anyway, it's absolutely worth it: try the brunch, the cakes, the lemonade... Everything is delicious, fresh and home-made.
Karin Cugusi: Formerly a Nazi bunker, later club that preceded Berghain. Beautiful space, great collection of artworks, amazing guided tours. The entry is cheap, but you need to book a visit few months before.
Capitol Building · Dorotheenstadt · 376 tips and reviews
VictoriaG: The dome is an absolute must if you come to Berlin. Book in advance on the official website and don't forget to take the audioguide when upstairs. Great panorama of the whole city!