Arf... Near Milan you should try Florence, 200km at the south. I heard it is beautiful as Venice!
ps: To close the Paris subject, I spoke about Arche de la Defense because of its architecture, but it is true it is a little offcenter and there is many other things to see before like Arc de Triomphe (I mentioned Champs-Elysées and not Arc de triomphe which is at the end, what an idiot I am..
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I confirm that travelling by in Paris is a true nigthmare, metro is a good alternative if you're used with that. I didn't think about the boat trip, maybe because I rarely went to Paris for travelling. I never try but it could be great