After La Mare à Piat, continue a little ways further along the same narrow path, before once again following Route Tournante du Cuvier Chatillon on your left, paralleling the path. Continue pedaling along this road that will lead you to a car park along the D142. Be very careful crossing this road. On the other side of the road, get off your bike to go check out down below the Grotte aux Cristaux. After your visit, head back towards the D142 and take the first path on the left, which you follow some 200 metres back to the car park. Careful, this path is best suited to mountain bikes; if you like, you can walk this short section.