North Germany with a weeks notice.

I'm a 19 year old guy who has had the prospect of solo travelling unexpectedly dropped on him.

As a result of several unimportant things happening I'm suddenly going to be left behind in Hamburg after a sports trip while the rest of the group flies home to the UK in just over a week. I said I'd find my own way home, but I thought it was too much of an opportunity to miss, so I'm going to stay for a few days in Hamburg before heading on to Berlin.

Main point time: In order to be in Berlin over a weekend I ended up booking for six nights (EastSeven Hostel). However, I'm starting to doubt if that's the best use of my time. I'm certain I could find many weeks worth of interesting and fun things to do in Berlin, but I'd rather not see a load of nice-looking places sliding past the coach window as I make a beeline for the capital.

Are there any places that you could recommend on the way there*, maybe staying for a night or two? Or is Berlin big enough (it's 10km from the bus station to the hostel!) and interesting enough to fill up five full days (and two half days)? Any recommendations from people who've been in a similar position? I'm game for just about anything as long as I don't end up hemorrhaging money.

*the "way there" is used loosely, anywhere between Hannover and the coast is fair game in my mind.