7 days till Berlin

I'll be at my hotel in Berlin in exactly 168 hours. My friends and I will probably sneak out, if our teacher won't allow us to go out and party. This is going to be my first sneak out, so it's very exciting.
Berlin itself is very cool too, and I look forward to ''smelling it'' and ''tasting it''. The people who have seen the movie Chasing Liberty (great movie) know what I'm talking about. ;-)

Have you ever been to Berlin? If so, where should I definitely go and what should I see?