We are staying near Les Halles Chatelet Station. What would be the best way for us to get to Versailles via RER? Do we need to go over to Orsay? Or can you catch the RER to Versailles from near where we are? Thank you.

From Châtelet les Halles you can take the RER B one stop south to St Michel, then transfer to RER C west to Versailles Rive Gauche. The first bit can also be done via metro; personally I'd be inclined to walk.

I also would be inclined to walk over the bridges as a start to my day rather than march at quicktime through the tunnels of Les Halles.

Be sure to keep your RER tickets handy, our train was 'spot checked' twice for tickets on the way back.

I also would just walk to St Michel and pick up the RER there . . . . .

Just be sure you board a train bound for Versailles Rive Gauche.

The walk from the RER station is fairly easy save for the cobblestones in the vast court yard.

I don't know that arriving early is the best strategy. We tried it that way; got there before the ticket booth opened.

For the first 10 minutes or so we had the place almost to ourselves, but the tour bus mobs caught at the king's bed chamber and before we could finish seeing it, the Hall of Mirrors was full of people.

There are various ideas on when to bet there. Some say late afternoon.
I don't know for sure, but our idea could stand improvement.

If the Châtelet les Halles complex is really the closest station to where you are staying, and you don't mind walking a bit, the advice given above about walking to St. Michel is good.

Then by all means, we shall walk to St Michel. Seems like a nice way to start the day. Thanks all!