locations

Hello,
My friends and I recently graduated high school last year, and we have decided that it would be a lot of fun to do a europe backpacking trip this summer. We plan to leave during may and stay for around 21 days. Now we’ve all been throwing around cities like Paris, London, Munich, Zurich, ect. But I was wondering if anyone could point me in the direction of around 5-6 cities that would make for an excellent trip.

We plan on going out and experiencing the night life quite a lot, but we also want to see the historic side of things.