Urgh, I meant Berlin, more specifically.
Ah, that happens to be the only large city in Germany I've never been to. :/ I'm afraid I can't give any first hand advice, but everyone I know tells me it's swarming with culture, (including
lots of artistic stuff and fun stuff).
In Germany in general I would recommend getting to know the people in a more intimate manner, if possible, rather than going to some really big events. The huge majority of Germans I met are extremely nice and friendly people, who will talk and drink a beer with anyone, and are fairly good at English, although they don't really trust their knowledge and therefore might need a bit of encouraging.
So, long story short - better go to a bar or a small-scale concert with anyone you happen to know and spend a day meeting people and walking through town with a beer in your hand (that's legal in Germany), rather than going to some stadium to watch a football match. Not that I would know of you planning to do any of those, it's just an example of the two extremes I mentioned above.
And make sure to take lots of pictures and upload them to the Internet!
Do let me know if you find any must-see/visit place - who knows when I might end up there myself.