Backpacking through Europe?

[hawthorne]

I wanna go backpack through Europe for around 2 months. I want to go to England (London) France (paris, nice) Italy (rome) greece (athens, greek isles) and spain (barcelona) for sure. Any other countries/cities i should go to for sure? or any specific things i should do in the cities? i am mostly looking for places i should go but i also just want any tips you have for me in general.... Thanks