Below is a post I provide to someone looking for ideas for planning a trip to Rome/Paris. Since it was under Travelers Helpline for Italy, I thought those on this section might be interested too.
When in Paris, consider a day trip to the Palace of Versailles. It's an easy train ride outside of Paris and will be a day you will never, never forget. Plan to go on Saturday or Sunday so that you not only experience the wonderfuly tour of the palace (audio guide is very good) and surrounding areas, but that you can also enjoy the Grandes Eaux and Jardins musicaux midafternoon (check their sight for last day in fall). This is where they turn on hundreds of fountains within the extensive gardens and pipe in classical music as you wander the grounds. You pay extra for this, but worth every euro and you should enter the gardens as soon as it starts because it is hard to see everything. Check out their website, http://en.chateauversailles.fr/discover-estate, and image this fountain turned on with water shooting up in the air and falling on the chariot and horses as they fight to try to come out of the water! There are many huge fountains like this and each is more beautiful than the other. The Fountain of Neptune is their most prized fountain & is turned on just before the garden closes, so be sure to get to that area early to find a seat in the grass! Their website doesn't capture all the beauty Versailles ! I didn't have time to see The Grand Trianon nor Marie-Antoinette's estate so I can't comment on whether they are worthwhile. Maybe others can comment on those