Set out from Dourdan station (RER line C).
(S/E) As you leave the station, take the road opposite you (south), and then at the end of the road, turn left down Rue de Chartres. Walk around Dourdan castle to your right (clockwise).
(1) At the southeast corner of the castle, take Rue de l'Abbé Gérard opposite you. Turn left down Rue Jube de la Perelle, and then right down a footpath with yellow PR (Petite Randonne – Short Hike) waymarks. Cross a river, go under a public building, and continue straight on, south-southwest.
(2) Take a right and immediate left to continue down Rue de l’Ouye. Cross the D116 and keep going straight on down a small road. Shortly after, take the marked footpath leading into the woods.
(3) Cross a small road and continue south along the path. Walk through Normont, ignore the path off to the left and the right and then follow the bend round to the left. Cross the Ruisseau de l’Etang de la Muette stream. The path then joins a track, follow it for a few metres to the left and then take a path to the right that bears south and then shortly after, southeast. Continue on this marked path until you reach a clearing with a water treatment plant at the end of it.
(4) Now turn right down an unmarked path that climbs slightly and leads to a crossing in the forest with a PR footpath (yellow waymarks).
(5) Turn right down the marked path called Route du Loup, and then turn left down Route de Caribotin. The path bears west and then turns south (ignore a path off to the right at this point).
(6) At the forest barrier, turn right and head downhill. At the bottom of the slope, head due west between the arable fields until you reach Ouye Abbey.
(7) Climb back up through the forest opposite you along Chemin de la Messe (signposted, red and white GR waymarks), ignoring any paths off to either side.
(8) When you reach the end of the woods, turn right down the path that takes you past the car park. Cross the D5 road, and walk downhill to cross a stream. Climb back up again opposite you, and then continue along the edge of the forest, ignoring any paths off to either side.
(9) At the car park, turn right down a wide gravel track. Keep going straight on (east-northeast) for 3km, ignoring the many paths off to either side along the way.
(10) At the roundabout of the D116, there is a pedestrian path just before a cycle path, and the church tower indicates the direction for Dourdan town centre. Walk down Avenue de Chateaudun, and then continue down Rue du Puits des Champs, Rue de la Basse Foulerie, and finally Rue de la Haute Foulerie on the right.
(1) Walk back around the castle to your left (anticlockwise), and follow the route you took on your way to get back to the station (S/E).