Pedestrian circuit of 15km in medium speed with slopes of 300m uphill and 300m downhill. Discovery of a geological reserve of the Essonne, sensitive natural space also conservatory of plants then valley of the Fox on the traces of an old river. A look at some polishers then Souzy-La-Briche and Arpajonnais. Then ascended to an acid environment to evoke the profession of carrier and valley of the Barley to join the station of Saint Chéron.