We stayed here for a couple of days. It's called Huttopia. It's a chain of green/ethical campsites throughout France. We stayed at the one in Rambouillet and used it as a base to get into Paris on the train for the tourist trail.
At Huttopia, the focus is very strongly on the environment, with all sorts of optional activities planned, plus huts and other facilities made from reclaimed materials. There's even a fresh-water swimming pool which looks great and completely different to your usual holiday poolside scene.
Also, this is good on what comes after green.