Many Americans doesn't realize or appreciate the complexity of Europe.
Indeed... I recently heard the rumor that Europe isn't even a county!
Beautiful landscapes, train stations, cities, zoo's, library, castles,nice architecture,bridges,historicals sites, waterfalls,mountains,nice cruises.. as you might understand, everything that makes a nice photo is welcome in suggestions!.
My top city list I'd go to for pictures: Paris, Rome, maybe London - it's obvious, but it's really the correct choice. The problem is that you have to stay in every city at least one month to get to know the atmosphere, but that contradicts having a train ticket. But since these cities are so densely packed with attraction's it's great to wear down your shutter. I live in Berlin, but in comparison it pales for photo-shooting. London might be an obvious choice because the people there are said to speak some kind of English dialect :->
If you should decide to come to germany, I strongly suggest you visit the so called "saxon switzerland"
... another +1, that's really beautiful and surprisingly not that commercial yet. You can visit the czech side, too, it border runs right though the national park.
And for nice rural shots go to or through southwestern Germany (the part with the castles and medieval city cores :-)). And Neuschwanstein sure is worth a shot, though the crowd reaches around the block: https://en.wikipedia.org/wiki/Neuschwanstein_Castle
... but really nice countryside around southern Bavaria and the Alpes.
Be sure to go see some of the countryside as well.
But if you visit other parts of eastern Germany and meet people with spanking short hair cuts who don't seem overly happy to see foreigners, be sure not to mention you're from the side that won the war (also see John Cleese in Fawlty Towers on this: "Don't mention the war :-)).
As a general advice I'd say stay clear from everything that's in the leaflet "Europe's culture in one week" like Salzburg, it's crowded, expensive and imho generally unpleasant. Another thing: If you should go to Berlin don't play the game "Under which of these three matchboxes is the ball?" while someone else streals your photo equipment, this is really a problem atm here :-o