From Courcelle to Lozère via the hillsides of the Yvette

Starting point and access: Courcelle-sur-Yvette station.
- RER - Line B, on the section between Paris and Saint-Rémy-Lès-Chevreuse.
Take exit 2 Rue Fernand Léger, on the platform heading from Saint-Rémy-les-Chevreuse to Paris (if arriving in the opposite direction, take the underground passage).

Yellow markings

(S) When leaving the station, follow Rue Fernand Léger towards the town centre. Cross Allée du Manoir on the left and you will come to a wider road, which is still Rue Fernand Léger. Follow this road to the left, ignore a road on the right and cross the Yvette. At the end, cross the main street (Rue de Paris on the left, Avenue du Général Leclerc on the right) and take the Ruelle d'Aigrefoin (dead end) opposite, slightly to the right. At the end of the tarmac road, go through a forest barrier and enter the Forêt Communale d'Aigrefoin.

(1) At the fork that appears immediately, climb the stairs on the right. Continue along a path that winds upwards. At the top of this climb, you will reach a crossroads (boundary stones).

No markings

Take the^second path on the right, with no direction indicated on the boundary stones. Walk north-east, pass under a high-voltage power line and arrive at a large crossroads (signpost, picnic tables).

Blue + yellow markings

(2) Take the^second path on the left, towards Magny-les-Hameaux.

Blue markings

At the crossroads, go straight ahead between plots nos. 20 and 19. At the next crossroads, take the^second path on the right, still towards Magny-les-Hameaux. Go down a steep slope (on a narrow section littered with tree trunks, you can take a parallel path on the right).

No markings

At the crossroads at the bottom of the descent (boundary stone), turn right towards Marais Bonnard. Continue on a slight downhill slope between the Bois des Grais hill on the left and the Bois d'Aigrefoin hill on the right.

Blue markings

(3) At a crossroads, turn left, cross a stream and immediately turn right (leaving the "Chemin de la Carrière" sign on your left). Continue eastwards, descending gently. Go through a forest gate and cross a small car park. Cross the D95 carefully and follow the path opposite between a meadow on the left and a hedge on the right. Cross one arm of the Mérantaise river on a^first footbridge and you will soon reach a^second footbridge on the other arm.

No markings

(4) Turn right and cross the river. Enter the forest and climb gently with a fence on your right. At the T-junction, turn right and follow a wire fence on your right.

Yellow markings

At the bottom of a slight descent and just before a small bridge, take the Chemin du Moulin on the left towards Saint-Aubin. Climb up a small valley lined with small rocks, with a stream bed below on the right. On the last few metres of the climb, the path is interspersed with wooden steps.

No markings

(5) At the top, at the edge of the fields, turn right and you will immediately reach a crossroads. Take the^first path on the right, leaving an EDF power station on your left. At the fork that appears immediately, turn left and follow a ditch on your left. At a small bridge on the left, turn right and, at the three-way junction that appears shortly afterwards, follow the Chemin de la Crête to the left. Stay on the stabilised path that winds through the shade.

(6) At the end (plot no. 74), turn sharply right and go down a steep path interspersed with steps. Cross the D306 (be extremely careful, as it is a very busy road) and continue downhill opposite on a path between two fences. You will come out at the CNRS site in Gif-sur-Yvette and find yourself back on tarmac. At the three-way junction, turn left and head south down a wide avenue ("only authorised passage"). At the end, take the pedestrian gate to the left of the central gate.

Red and yellow markings

Continue straight ahead along a car park. Cross Rue Neuve and then Rue Henri Amodru to arrive at the foot of the post office.

(7) Follow the street to the left. After about 100 metres, turn right and walk past the town hall on your left (marked Château de l'Ermitage on the OSM map). Walk past the war memorial and continue straight ahead on a stabilised path.

No signposts

At the next crossroads, turn left and walk along a pond on your right (small island with a statue). At the end of the pond, first turn right then left and walk along a covered market on your left. Shortly before a perpendicular street, turn right and cross a car park.

Red and white markings

At the corner of the municipal library, turn left and follow Chemin du Bras Mort, which goes through a tunnel under a street and along a stream. Then turn left between two fences. At the^first junction, go straight ahead and you will immediately come to a^second junction.

(8) Take the footbridge over the stream on the left and follow Chemin du Bras Mort. Continue straight ahead on this paved path lined with street lamps and ignore all turnings on the left. Walk along the right-hand side of the Bassin de Gif-Bures, a large wetland area with a few reed beds. Further on, first turn right then left with the path to cross the stream again and continue on a gravel path at the top of a dyke.

(9) When you reach a small building, turn left and cross a small car park. Immediately turn left, cross the Yvette and follow Rue de la Prairie (signposted further on). At the crossroads, go straight ahead into Rue des Bleuets. Take the^first left, Rue des Coquelicots. At the end, turn right onto a footpath and follow the river on your left.

No signposts

At the end, take the bridge over the river and follow Rue du Docteur Collé. Cross Avenue de l'Yvette on the left, then Avenue du Square. Walk up the street alongside a school on your right. At the T-junction, turn right onto Rue de la Guyonnerie. After about 100 metres, cross the street at the pedestrian crossing and take the path on the right that runs parallel to the street.

Red and green markings (old)

(10) After about 100 metres, turn left and go through a forest gate. At the fork that appears shortly afterwards (plot no. 29), turn right.

Red and green markings (old) + yellow

Ignore a path coming from the left and head east, crossing plots 26 and 25 in succession.

No markings

Ignore a path on the right and then a staircase on the left and continue straight ahead towards the east (plot no. 22). Ignore a path on the right and, after about 150 metres, you will come to another fork (tree marked with no. 10 high up on the left).

(11) Turn left onto an uphill path. Pass directly below a reservoir, ignore a trail on the right and continue climbing steeply between small rocks. You will reach a flat area (plot no. 9; picnic table).

Yellow markings + red and green arrows no. 5

Climb the steps on the left. At a sort of landing, take a path on the right. Go through a forest gate, come out onto a small road and follow it to the right. At the intersection that comes up quickly, turn left towards the N118. At the stop sign, turn left and head towards a water tower. Then turn right onto Chemin de la Voie Verte and pass at the foot of the water tower.

(12) At the end of the tarmac road, at the corner of a fence, turn right onto a path and walk along a field on your left. Enter a wood and go downhill. You will come out onto a narrow street and, at number 1, squeeze through a path on the left between a private car park on the left and a house on the right. Cross a street, go down a flight of steps opposite and continue along a path. You will come out onto a street. Turn left twice towards Passage de Corbeville. Take the pedestrian tunnel under the N118. On the other side, turn left onto Chemin du Guichet (tarmac). When the street turns right, continue straight ahead on a path and go uphill. After a right-hand bend, climb a staircase.

(13) At the top, take the fairly flat path on the right and ignore the steps on the left. Ignore a path on the right and you will soon come to a crossroads (gate on the left). Continue straight ahead and go through a metal gate. At a three-way junction, follow a faint path to the right towards a red-plastered house. You will come out onto a street. Continue for a few metres and take the entrance on the left into a fenced-off wood. Immediately turn right, walk along the fence and, shortly afterwards, go down a wooden staircase that leads into the old Troche quarry (^first information table).

(14) Walk along the sandstone blocks on your left (picnic tables). After a^second information board and before a footbridge, climb a staircase on the right. You will come out onto a cement path. Follow it to the left and take the footbridge. Climb another staircase and you will come to a T-junction. Follow the tarmac path to the right. Pass an information panel about the quarry and continue straight ahead. Walk past the Ferme de la Vauve on your right and a ditch on your left. At the "give way" sign, turn right.

Red and white + yellow markings + red and green arrow no. 5

(15) Immediately turn left onto a stony path. Go around a riding centre on the right and follow a dirt track that winds through the undergrowth (potentially wet sections). Further on, walk along a fence on your left.

Red and white markings

At a concrete crossroads, turn right. Go down a staircase that soon turns sharply to the left. You will come to a concrete path interspersed with steps. Follow it to the right and downhill. Continue along a narrow lane and continue downhill. At the T-junction at the bottom, turn left and you will soon reach Lozère station (E).

To return home:
- RER - Line B, towards Paris (immediate access) or Saint-Rémy-lès-Chevreuse (take the underground passage or footbridge).

Train timetables: consult the Transilien website.

For motorists:
Park in the car park of one of the two stations and make one leg of the journey by train.

Hiking boots required.

Bar, restaurant and shops in Gif-sur-Yvette (7). Picnic tables in several locations indicated in the description.

Detailed map useful (at least the one accompanying this description). For tracking on a smartphone, download both the IGN and OSM maps, the latter being more up to date.

Hike completed by the author on 29 January 2023.

Pleasant forest trails between (1) and (3), (4) and (6), (10) and (11).
- Gif-Bures basin.
- Former sandstone quarry at La Troche, now converted into a climbing school (14).
- La Vauve farm (15).