There's too many places for me to list without it just being a list of everywhere I've been, and that would be stupid. So instead I'd say the place that I expected the least from and got the most out of was Prague, in the Czech Republic.
Didn't know anything about the place before I went but the City is like something out of a fairytale. The city is beaming with beautiful architecture which is hundreds of years old and largely survived WWII (unlike many other European cities,) they've got great food, great beer, absinthe bars, fantastic museums, beautiful squares, and unique monuments and statues. They've also got great music clubs, dancing clubs and bars, and lots of stuff to do on the more mild tourist attraction side of things. The people are very friendly and best of all it's one of the cheaper places you can visit in Europe. I spent 11 amazing days there a few years ago and I've been dying to go back every since.