Which article to use before Europe?

You don't need an article before "Europe" when referring to the continent as a whole.

Examples:

* Europe is a continent.

* I traveled through Europe last year.

However, you would use "the" if you are referring to a specific part of Europe:

* The European Union is a political and economic union of 27 European countries.

* I visited the south of Europe this summer.

In general, use "the" when referring to something specific and "no article" when referring to something general.