When your European cruise docks in Normandy, France, you'll have the opportunity to book a shore excursion that continues on to the world-famous city of Paris. It'll take some time to reach the city, so you should prioritize the attractions that you want to see. It's virtually impossible to do Paris in a day, but with a little planning, you can certainly try.
Even if you had all day, you still might not be able to experience everything that the massive Louvre has to offer. Famous exhibits like the Venus de Milo and Mona Lisa are certainly worth a visit, but keep in mind that the Louvre also boasts an extensive collection of Ancient Egyptian artifacts, Islamic art, Greco-Roman statues, paintings from all eras and just about everything else that could possibly fit in a museum.
The Eiffel Tower and Arc de Triomphe are probably the most recognizable sights in Paris, and you'll be able to scale both of them in order to get a better view of the sprawling city. Those who spend time at the Arc de Triomphe may also want to explore the Champ-Elysses, perhaps the most famous street in Paris, if not the world.
Finally, don't forget Notre Dame Cathedral. This beautiful structure is certainly impressive from the outside, but be sure to allocate some time for the interior as well, as the workmanship on display here is simply beautiful.