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Starting point and access: Saint-Quentin-en-Yvelines station.
- RER - Line C, terminus of the section coming from Paris via Versailles-Chantiers.
- Transilien - Line N, on the section between Paris-Montparnasse and Rambouillet.
- Transilien - Line U, between La Défense and La Verrière.
Take the Porte Charles de Gaulle exit.
Red and white + red markings
(S) On leaving the station, go straight ahead. Cross a wide avenue (at a pedestrian crossing) and continue straight ahead onto an esplanade. After about 200 metres, turn right and head due south along a path with small ponds in the middle (under construction in October 2020; follow the signs). Go round the left-hand side of a square featuring a maze of vegetation. At the corner, turn left. You will reach a concrete path.
(1) First turn left then right and enter the Bois des Roussières. Stay in the undergrowth and above a pond for about 1 km.
(2) At a crossroads, turn right, go down a flight of steps and leave the woods. Immediately go down a flight of steps on the left. Then enter the tunnel that passes under a four-lane road. Shortly after exiting the tunnel, turn right then left to reach the Bièvre river (on your right) and come out onto a road.
Cross the road and take a path through the undergrowth running parallel to the road. Join this road at a junction and continue straight on in the same direction. After a few dozen metres, turn right (small steps) then immediately left. A path built on a wooden footbridge allows you to get as close as possible to the river.
(3) Pass the Fontaine des Gobelins (information panel). You will reach the western tip of the Étang du Moulin au Renard.
No signposting
(4) Leave theGR®® by turning right then immediately left. Walk along the left-hand side of the pond for about 1.5 km. At the other end of the pond, turn left into the car park. At the end, follow a small tarmac road to the right (no traffic). Continue straight on for about 400 m.
(5) Look for a flight of steps on the right and go down them to reach the edge of the Étang du Val d'Or. Then turn left and walk along the right-hand side of the pond. You will come to a car park. Go straight ahead into a tunnel that passes under a four-lane road. Follow a path that descends slightly and goes round a sewage treatment plant on the left.
Red and white markings
(6) At the crossroads (elevation 115), rejoin theGR®® and follow it to the left along a wide path through the woodland.
(7) At the fork at the corner of the Étang de la Geneste, continue straight on with the pond on your right. At the end of the pond, turn right onto the embankment until you reach a clearly visible water regulation facility. Then go down a flight of steps on the left to join the course of the Bièvre. The path winds through meadows, first along the right bank of the Bièvre and then, after crossing a bridge, along its left bank, until you reach a car park in Buc.
(8) Cross the road, walk past some buildings and take a path that winds its way between houses and gardens, with the Bièvre once again on your left. Turn left and cross the Bièvre again, then turn right. Walk alongside a small pond and head uphill towards the arcades of Buc, which can be glimpsed through the foliage. After turning sharply left, cross the D393 (take care, as there is heavy traffic).
(9) Pass under the arcades of Buc (information plaque) and go down a steep slope. Continue along the path, bordered by woodland (on the right) and pastures (on the left). The path turns left and goes round a large farmstead (horses). Just before a road, turn right onto a path that runs alongside the Bièvre again (on the right).
Red and Yellow + Blue + Red markings
(10) At the road, let theGR®® head off to the left, turn right and cross the Bièvre again. Turn onto the first path that starts on the left behind a forest gate (ignore the Red Cross and Yellow Cross). Join theGRP®® coming from the right, then follow a boundary wall on your right.
Blue + Red markings
(11) At the corner of the wall, continue straight on between two meadow fences (let theGRP®® head off to the right). Pass another forest gate, then climb slightly through the undergrowth with a garden fence on your left. At the corner of the fence, turn left as you go downhill. Go through the gate and cross the railway line ( be very careful; look both ways carefully) . Continue straight ahead, leaving a pond on your right.
Red and white markings
At the start, you will also see blue, green and red markings; stick to the red and white markings of the GR®®.
(12) At the junction, turn right (do not cross the Bièvre). After about a hundred metres, leave the river and walk across the meadows. Cross a small road and rejoin the Bièvre on your left. You will then come to a road near a roundabout on the right.
(13) Go round the roundabout on the left and cross Avenue Jean Jaurès. Then cross the railway line at the level crossing. Pass a small unpaved lay-by and take a path on the left (small boulders). You’ll reach the Bièvre and follow it on your right. As you approach some buildings, turn left to cross a car park and then a small square.
No signposting
(14) Cross Rue Oberkampf at the level crossing, take the path opposite and follow the railway line on your left. Go straight on and, at the end, continue along a street. At the Stop sign, turn left and cross the railway line. Cross the road at the next pedestrian crossing, before it bends to the left.
Red and white markings
(15) Then take the access road to the INRAE centre opposite. Just before the entrance gate, take the cul-de-sac on the right leading to the equestrian centre. After a few dozen metres, leave the road on the right, cross the Bièvre and take a path that starts at the foot of a fence with concrete posts. Follow the path that zigzags between a hedge, behind which lies the railway line (on your right), and the meadows of the equestrian centre and then the INRAE centre (on your left). After about 1.5 km, you will reach a road near Vauboyen station. Make the first turn right then left to rejoin theGR®®.
(16) Follow (east-southeast) the path running alongside the railway line. After about 800 metres, you’ll come to the Bièvre river on your left. Continue straight on. The path is lined with houses and gardens before becoming a narrow lane. Cross Rue des Petits Ponts on the left, then Rue des Ponts.
Red and white + yellow markings
(17) At the roundabout, turn left into Rue du Petit Bièvres. Cross this street at the pedestrian crossing near No. 11. Continue up the street for a few metres. Just before the sign for the Bièvre, turn right and head down to a path along the riverbank. Follow the Bièvre on your left.
At the signpost, continue straight on towards Igny. After a left-hand bend and a right-hand bend, cross the Bièvre and follow it on your right. At a junction (bridge and buildings on the right), continue straight on, keeping the Bièvre on your right. After about 250m, cross the Bièvre again and move away from it, walking between two fences. At the T-junction, at the foot of the N118, turn right onto Rue de la Gare.
(18) Turn left onto Rue de la Gare and go under the N118 bridge. Turn left at the foot of a pylon and immediately turn right onto the Sentier Maurice et Alain-Victor Marchand (information sign, forest gate). After a few short bends, reach the Bièvre (footbridge).
(19) Follow the river on your left (do not cross it) and continue until you reach a small road. Cross this road and continue along the Bièvre, now on your right. Cross a bridge and you will find yourself on the other bank. Continue for about 500 metres.
Yellow markings
(20) After the path bends to the left and before a bridge (sluice system), turn right. Climb slightly up a path, pass through a forest gate and reach Igny station (E).
To get back home:
- Transilien - Line V, towards Massy-Palaiseau (direct access; connection with the RER B) or Versailles-Chantiers (take the underpass; connection with RER Line C and Transilien Lines N and U).
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