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RER line C. The station is the terminus of a route from Paris via Versailles-Chantiers.
”Red and White markings”
(S) At the exit of the station of St-Quentin-les-Yvelines, go straight ahead. Head across a wide avenue (pedestrian crossing) and continue ahead over an esplanade. After 200 metres, turn right and follow an alley due south with small water pools in the middle. Go around a grove to its left and reach a small road.
(1) Cross the road and head into in the Roussières woods (with a sign). Staying in the underwood and above a lake for about 1 km. Turn right and leave the woods, immediately turn left (stairs) and and go through the tunnel under a 4-lane road.
(2) Shortly after the tunnel’s exit, turn right and then left to follow the Bièvre river (keep it on your right) and reach a road. Cross the road and head along a path through the woods parallel to the road. Join this road at a crossroads and continue straight in the same direction. After a few metres, turn right (small steps) and then immediately left. A paved road over a wooden bridge lets you get closer to the river.
(3) Head on to the Fontaine des Gobelins (with an information panel). Arrive at the the Moulin à Renard lake.
’’No Markings''
(4) Leave the GR® turning right, and then immediately left. Along the lake on the right bank for about 1.5 km. At the other end of the lake, turn left into the car park and then right onto a road. Continue straight for about 400 metres.
(5) Once at the Val d’Or lake, go down the stairs that lead to the bank and walk along the lake on its left bank. The path ends at a car park. Go straight ahead into a tunnel under a 4-lane road. Lead to a path that bypasses the water treatment plant, head down and take a wide turn to the right.
”Red and White markings”
(6) At the crossroads of several paths (marker 115), we find the GR®, which follows a broad alley through the underwood.
(7) At the junction at the corner of the Geneste Lake, go straight ahead and keep it on your right. After the lake, turn right at the dyke to an easily spotted water flow regulating installation. Turn down to the left (on stairs) and follow the course of the Bièvre. The trail winds through meadows, first on the right bank of the Bièvre river then, after crossing a bridge, on its left bank as far as the car park in Buc.
(8) Cross the road, walk along the buildings and head along a path that winds between houses and gardens, keeping the Bièvre river on your left. Turn left and again cross the Bièvre river, then turn right. Along a small pond and climb towards the arches of Buc that can be glimpsed through the leaves. After a sharp left turn, cross the D393 (with caution, the road is busy).
(9) Pass under the arches of Buc (with its information sign) and down a steep slope. Continue on the path on the edge of the woods (keep it on your right) and pasture (keep it on your left). The path turns left and goes around a large farm (horses). Shortly before a road, turn right onto a path along the Bièvre again (keep it on your right). Take a road to the left towards the railway bridge.
(10) After crossing the railway bridge turn right into the street through Les Loges-en-Josas. After 400 metres, turn right down a small street which heads downwards and becomes a path. Before the end of this road, turn left, walk through meadows, crossing a small road to return to the Bièvre river, keep it on your left as far as a road near a roundabout with median.
(11) Cross the roundabout and the railway (level crossing). Then head on to a path on the left that meets up with the Bièvre river. Arrive in an alley, which opens into a small street (level crossing to the left, and the church of Jouy-en-Josas at the end of the street on the right). Turn left and, immediately after crossing the rail tracks, turn right.
’’No Markings''
(12) After 200 metres, to avoid a long paved trail, leave the GR® (the latter portion on the right and cross the railway again). Head across the street that leads to the INRA centre (with a sign that is impossible to miss). Before the barrier, take the impasse that leads to the equestrian centre (there is a sign). After a few tens of metres, take the path to the right that winds through a hedge behind which the railway line is located (on the right hand side) and the fields of the equestrian centre and the INRA centre (on the left hand). After about 1.5km, reach a road at the Vauboyen station. Make a right-left dog-leg to meet up with the GR®.
”Red and White markings”
(13) Follow (heading south-east) the path along the railway. After 800 metres, find the the Bièvre river which is on the left hand. Continue straight ahead. The path is lined with houses and gardens then becomes an alley. Cross the Rue des Petits Ponts and the Rue des Ponts to reach a roundabout. Continue slightly to the right on Avenue de la Gare, and pass the aforementioned station.
(14) Continue straight ahead. Pass under the bridge of the N118. After a left turn, head immediately to the right onto a path that leads on to the right bank of a lake.
(15). Join the Bièvre river and follow its right bank to a small road. Cross this road and continue on the left bank of the Bièvre river. Cross the bridge to end up on the right bank. Continue for about 500 m.
’’Yellow Markings''
(16) After a turn on the path to the left before a bridge (gate system), turn right. Climb gently up a path, pass a forest fence at the Igny station (F).
To head home:
RER line C, either to Versailles-Chantiers or towards Massy with connections to other lines.
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