Because you mentioned you were new to this, I'll chime in.
As the posters have said, Versailles is a slam-dunk, as independent travel goes.
I think a few of the more experienced replies here are hinting, asking, about how badly you really want to go to this location, Pierrefonds? It sounds like it's a bit on the outskirts, a hop-skip-and-jump from the main routes, and in my experience, it could really help to have some Europe travel skills learned on this one, should things not work out exactly as planned. I've been there, with stories to tell. And every independent trip I've done, there's always something that doesn't work. With more travel skills under your belt, you'll have several "plan Bs" that you can execute when plan "A" flops.
I don't mean to dampen your dreams - it may work out just fine, but if you research some more, you may find another place that is just as interesting - and is also easier to get to/from. You may even find something better! That's been the case with my wife and I. Europe has so much to see and do that you can always find fun things nearby.
For your first trip, you may want to stick to places well-documented in Rick's guidebooks - you'll still have a great time!
Just a thought.