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Departure from Bures-sur-Yvette station (RER B). (For another departure from Gif-s-Yvette, see "Practical information".)
(S/E) Start not signposted. Coming from Paris, cross the tracks. Take the "impasse de la Station" exit. Take the street that runs perpendicular to the tracks (north), then the first left (Passage du Villevert, west). Go straight ahead into the Parc de la Grande Maison (if it is closed, go around it on the right). In the park, walk straight ahead for 150 m, then turn right at a right angle (north) to leave the park in front of the market. Follow Rue Charles de Gaulle to the left until you reach a roundabout. Take Rue du Docteur Colle diagonally to the right, with a small river on your left and a football stadium on your right. Take the first left, Rue des Bleuets, then Rue de la Prairie opposite until the end.
Red-green signpost no. 4.
The route is well marked and generally easy to follow, but you should watch out for unexpected changes in direction and missing markings in some places.
(1) On a footpath, turn right at signpost no. 4. Go around the floodplain (Bassin de Bures-Gif) on the right. Turn right and cross a stream, then turn left. At the fork that appears immediately, turn right and go slightly uphill. Join Rue du Hameau de la Févrie, climbing slightly northwards, then turn left into Rue de la Févrie. Turn right and cross the fairly busy Rue Gustave Vatonne to join a path straight ahead (north). Climb steeply straight ahead (stairs).
At the top, take the path to the left (west) along a stone wall, the Route des Plants du Moulon, which follows the edge of the plateau.
(2) When you reach a paved road (D306), follow it to the right for 50 m. Then cross the D306 ( very busy road). Paying close attention to the zigzagging markings, follow a path (west) then a trail on the right (north).
(3) Before reaching the fields, turn left (south-west) and then immediately right towards "Chemin de la Crête" (west, then north-west). Continue on flat ground. At a fork, turn right.
(4) Cross a small stone bridge over a stream, then turn left onto Chemin de la Lisière.
(5) At a gate, you will see a clearing at the edge of a field with a bench. Turn left (south-west) towards "Chemin de la Rigole". Do not follow the stream, but keep right along a fence, slightly downhill. After 400 m, take a path downhill on the right. Pass a few houses, join the D306 and follow it to the right for 50 m.
(6) Turn right onto Chemin des Fonds Fanettes, towards "Chemin du Moulin". Stay on the flat. Keep left, alongside a few properties.
(7) At a crossroads with a bench, turn right uphill (signposted "Chemin du Moulin vers Saint-Aubin").
(8) At the top of this climb, turn left, signposted "CR5 Chemin de la Fontaine Billehou, vers le Billehou". Follow the edge of the plateau, which is fairly flat, heading west. After one property, the path descends; halfway down the slope, take a flat path on the right (north).
(9) At a gate, turn left downhill (signposted "CR8 Chemin du Bois. vers le Canal", north-west). On a small tarmac road, cross the small Norman-style hamlet of Le Canal with its little river. Continue along the road until you reach a crossroads. Follow the larger road on the right (Route de Gif) for about 100 metres.
(10) Opposite No. 37, take a path uphill on the left (poorly marked, uninviting, steep and slippery: if necessary, take a wide detour to the right). At the top, take a wide dirt road to the left. Stay on the edge of the forest plateau, heading south-west then west-north-west.
(11) At a crossroads, go straight ahead towards "Chemin de Voisins-le-Cuit" (north-west), downhill. 300 m further on, at a bench, take a path downhill to the left at an acute angle (south). Join a tarmac road and follow it to the left (Impasse de la Petite Barrerie). Cross the village (which has a Norman appearance) of La Petite Barrerie. Cross the Route de Gif, then cross a wetland on some planks.
No signposts
(12) At the Mérantaise river, turn left. Cross the river and follow it on your right. Ignore a wooden bridge on the left and cross another branch of the river. Continue west.
Red-green signpost no. 4.
(13) Cross the Route de Gif (D95) at a car park and continue straight ahead. At the "Carrefour de la Carrière" sign, continue straight ahead, at the bottom of the valley, along a wide dirt track that climbs slightly (west) for 600m.
(14) At a crossroads, at the sign for "Forêt Départementale du Bois des Grais", turn left at a 90° angle uphill (south-west). At the top, at the crossroads of plots nos. 11-20, turn diagonally left, under no. 20.
At the crossroads of plots nos. 19-20-28-29, turn left (east) into a wide lane that quickly turns south-east. Cross two perpendicular paths. At the end of the lane (rubbish bin; elevation 149), turn left downhill (east). Do not take a path coming from the left and continue east. At the T-junction, turn right. Cross a small road and walk along a cemetery on your right. At the end, cross the D306. Be careful.
(15) (Signpost missing) Follow the road to the left (east) parallel to the D306 and pass a gymnasium. Turn diagonally right onto the path that cuts across the lawn. Between the houses, go down a path on the right (stairs). At the paved road, turn right towards "Centre ville". Cross a stream and turn left towards "Centre ville" to go around the flood basin.
(16) At the "Bassin de Coupières" sign, turn left at a 90° angle and cross under the road (Rue de la Croix de Fer) via an underpass.
For several kilometres, follow signpost no. 4 on the concrete path along the Yvette, heading east, alternating between the two banks.
(17) Turn right in front of a school, at a sign for "Jupiter", to cross the Yvette, which you will cross again 200 metres further on. Follow the river. Ignore the sign for "Gare de Gif Centre", but take the underpass under Rue Alphonse Pécard. Continue for 200 metres.
(18) Turn right (let theGR®® continue straight ahead). Join the main branch of the Yvette. Turn left and follow the river on your right and a large green meadow on your left. There are some pretty houses on the opposite bank.
(1) After the "Bassin de Gif-Bures" sign, turn right onto the path you took on the way there and follow it in the opposite direction to reach Bures-sur-Yvette station (S/E).
Visorando member
Easy 
Association / Club / Walk leader
Very difficult 
Difficult 
