I was lucky enough to spend a term in Paris when I was twenty. I don't remember climbing a lot of steps as I'm lazy, and even caught the metro up to Monmartre. Even the fact that it's inhabited by Parisians can't take away from the beauty of the city though.
My suggestion for a romantic weekend would be Florence. I went there for the first time last year, after seeing my best friend Milly in Milan and before going down to see another friend in Rome. You can walk everywhere, and it's flat. The buildings are stunning, and the Duomo is a Renaisance marvel of engineering. The square filled with statues, including Michelangelo's David, made me cry. I can't remember the name of the square, but you can't miss it, and it's in the film A Room with a View. Fantastic places to eat, and if you are not there for a romantic weekend with your partner, some wild nightclubs.
