I went to Italy last year, Rome was super cool for old stuff and the vatican. Cool to just be in the city... but it is a big city, so has big city drawbacks like anywhere else. Haven't been to venice, but my dad has, and he said if you've seen a movie with venice in it, you've seen venice. My dad also has the propensity to be a curmudgen, so take that with a grain of salt. Feel like I've heard the same thing about venice form others though. It also floods there all the time, so don't wear your nicest shoes. Florence was in a beautiful part of the country, I would try to make it out that way for the art. Pisa is close too... that was fun to visit. Seriously don't go down to Naples. It made me think that's what Rio de Janero must look like, slums and all. The place was a dump (from what I could tell).
Amsterdam is the tits. In more ways than one, lol.
If you are into history and art, I think London is the place to check out. They got lots and lots. All the stuff you'd ever want to see artiifact wise is in the british museum. And it's free to go in. The national gallery is cool too if you like paintings and such. There's parts of the old wall all round the city, the financial district is cool to be a tourist in... it's so old. There's Westminster Abbey you could check out, that's wild.
My wife says Salzburg is beautiful, it's surrounded by mountains and is just picturesque. It's really old and has history, it's where Mozart grew up, there's tons of big squares everywhere, and there's a river and you can walk everywhere, and it's hilly and I really love it. (wife's words)
Duchieman who used to hang out here a lot went to Budapest and said that was a great experience.
Istanbul is by all acounts amazing.
I have visited Copenhagen and went across to Sweden. It wasn't too exciting up there.
That's what I got.
And if you want to go to another planet and be there all by yourself, Eastern Iceland is the place to be.