I would do Paris in two days. I have been there half a dozen times -- trips ranging from 48 hours to 8 days -- and find the city super easy to navigate (you can practically walk from one end to the other) and you can actually SEE several sites (Eiffel Tower, Arch D'Triumph, Notre Dame, Pont Neuf, Tuileries Garden) while walking around....AND visit the Musee D'Orsay or the Louvre for a set time (you can do 1 hour or 4 hours), and you even have time for pastries, a cafe or two, and a bistro for dinner. I am sure you can find a two-day itinerary online that would suggest how to navigate. And there's always the Bateau Mouche (the boat on the Siene) that you can catch and ride from one end of the city to the other to orient yourself when you get there. My favorite museum, Picasso, is fantastic, too.