What are the best European cities to earn euros while you travel?

I am trying to find a list of at least 10 European cities that are great for earning euros as you travel, as part of an article I am wanting to write. The problem is that I can't seem to find any useful information on this topic. Anyone know the best cities? How do you earn?

Public Comments

1. Since you almost always need a work visa to earn money in Europe and can't work when you only have a tourist visa, that may be why you're having a tough time finding any information on this subject. About the only way anyone is going to make money without a work visa is to do something illegal, either work without a work permit, or work in an illegal field, ie: drugs, etc. And if they do they may be reluctant to talk about it.