From PARIS and CHARLES-DE-GAULLE AIRPORT to SAINT-RÉMY-LÈS-CHEVREUSE: RER B southbound, stop at "LE GUICHET" station and walk to the bus station, take bus n°269-02 to SACLAY, stop at "L’ORME DES MERISIERS".
Or RER B southbound to Massy-Palaiseau, then take bus n°91-06 (on your right when you go outside Massy RER B station - 50m walking) DIRECTION to SAINT-QUENTIN GARE, stop at “L’ORME DES MERISIERS”.