Layover at Charles DeGaulle

Buy a one-day, zone 1-6 Paris Visite pass (€18.50). It will get you to Paris and back on the RER B and will cover all your metro, RER, and bus rides while you're in Paris. Be aware that the RER B line divides northeast of Paris so be sure to get on a train that is going to CDG when you're ready to return to the airport. Also be aware that there are two RER stations at CDG. For more information, including photos, go to the Parisbytrain site.

You could take a Balabus tour or a Batobus tour. For either one you can get on and off as often as you wish.

Thank you ~ very helpful information!

The RR runs two or three times an hour and stops in the heart of the city near Notre Dame, so you will be within easy walking distance of a lot of must-see attractions on the islands and left and right banks. Budget about an hour, including wait times for the RR trains and at least two hours, three is probably safer, to go back through security at CDG. You may find yourself with only about half the layover time actually available for sightseeing, but that should be plenty. The museums are close, but don't waste a lot of your free time standing in lines. Besides, you will probably enjoy exploring central Paris on foot and spending some time in a sidewalk restaurant. Sure that is touristy, but so what!
After your trip, please report back on how the Paris layover worked out. Now that Air France is offering the Paris layover option for trips between the U.S. and other European cities, I am trying to decide between an overnight layover with Air France or frequent flyer miles with Delta on our next trip.

Thanks for your advice ~ I'll let everyone know how it works out when I return!