If you only have 24 hours then I wouldn't do Versailles...it's a full day trip to be even remotely worthwhile. If you're up for it physically, I would just "WALK" and take in the sites. Take the metro to Ille de la Cite and start at Notre Dame, see the inside of the cathedral but don't go up the Towers unless the line is very short to non-existent, then walk over to St Chapelle and DO go see the stained glass. From there, walk on over to the Louvre, if you enjoy art, then take the walking tour (about 1-1.5 hours).
>From the Louvre, head up to the Opera House and again you can have a quick tour here. From there, walk back down to the place Vendome and then up the Champs Elysees to the L'arc de Triomphe. There are some nice restaurants in the Opera House neighbourhood if you want to stop for lunch, otherwise, if your budget permits, have lunch at a cafe on the Champs Elysees. A restaurant that we ate at on the Champs was called Chez Clement, part of chain, but reasonably priced and very good food. It's within a block or two of the Arc, on the Champs Elysees on the left hand side as you approach the Arc from the Louvre/Place Vendome.

>From here, walk over to the Eiffel Tower, you can go up if that's something you want to do, again I'd gauge things by the lines. From there, walk along the Champs de Mars towards the Ecole Militaire and then hang a left and head over to Invalides and Napoleon's tomb. Nearby, is the Rodin Museum, a great experience, and they also have a nice outdoor cafe that you can enjoy a cold drink or coffee.

This should pretty much use up the best part of a day, you'll be tired, but (I think) happy.

Regards,

John Wiernikowski Hamilton, ON CANADA