Start at Brunoy train station (RER line D, on the stretch between Melun and Paris-Lyon).
(S) Upon leaving the station, take Rue de la Gare opposite (bar/tobacconist at the beginning of the street on the right). At the end of the street, turn right into Rue Philipsburg and go past the town hall. After the square, turn left into Rue Pasteur then immediately right onto Rue Saint-Nicolas. After a few metres, turn left into a cobbled street then right alongside the church. Head down some steps and find yourself at the foot of the stairs leading to the church door.
(1) Turn left onto Rue de Montmartel. After a bend to the left, pass Rue Pasteur and reach a crossroads. Turn right in the direction of "Talma" (sign). Head onto Perronet Bridge and cross the first stretch of the river (at the old mill on the right). Do not cross the second stretch of the river but, immediately after the first one, turn left towards a wooden hall to reach an island in the middle of the Yerres. Veer right to quickly reach the bank of the second stretch of the Yerres: a menhir named "La Pierre Frit" is on the opposite bank (inaccessible).
(2) Head to the east on a concrete alley (not depicted on the 1/25000 map but visible when zooming in) and stay closer to the river keeping it to your right. Ignore a bridge on the right (not depicted on the map) and then veer slightly to the left to reach the foot of the railway viaduct (marker post).
‘’Yellow markings (sparse)''
(3) Do not cross the viaduct, instead turn right at a right angle, in the direction of the “Forêt de Senart." Walk along the base of the viaduct to your left and then take the underpass (admire the maritime decor). At the end of this passage, turn diagonally to the right (paved ally doea not appear on the map). Arrive at a bus shelter, follow Rue Sainte-Geneviève on the right. At the next junction turn left into Rue de l’Espérance. After a few metres, turn right (small steps) and then immediately left. This street makes a bend to the right and goes up to a large car park ("Do not enter" sign visible from afar). Turn right onto Rue du Maréchal Ney. At the end of the street, after passing a 20 km/k speed limit sign, turn left onto a small asphalt path and reach a wood baffle leading to the forest of Senart.
(4) Immediately after the chicane, take the left path and after a few metres take a path going between forest plots No. 183 (formerly 175) and 182 (formerly 174). After a hundred metres, find a trail on the left to a big tree with two barrels. Be attentive, the Yellow arrow indicating a left turn is not visible; if you reach the place where the trail widens considerably and has been stabilised with white pebbles, turn back. After turning left, turn immediately right, passing in front of the tree with two trunks along a small ditch on the right hand. Cross a road (take care) and continue across a path that goes diagonally to the left then winds along the left hand of a deeper trench than the last. At a T-junction, turn left onto a wider sandy path.
’’Yellow and Yellow/Red markings''
(5) At the first junction, continue straight ahead. At the second intersection, take the second road on the left (north-east). Ignore the start of another branch of GRP on the right and continue in the direction of Boissy (sign on a tree) and then veer left to cross a road again (take care). Continue opposite, head down, go under the railway bridge and emerge onto a street that goes down again.
Yellow + Red markings
Here there are non-GRP markings.
(6) Cross the Rue du Gord, leave the GRP from right (the footbridge over the Yerres does not appear on the map) and cross a stream over a wooden bridge. Head around the football field on the right. At a junction, take the path on the right (not shown on map) and stay close to the river on your right hand.
(7) Take the bridge on the right to cross the Yerres. At the end of the bridge, contrary to what is suggested by the purple line on the map, turn immediately left and follow the river keeping it on your left. Pass under the bridge of the road.
(8) Just after the bridge, leave the red markers and climb up on the right continuing along the river where it quickly leads to a small menhir. Continue close to the river (not shown trail on the map) and then deviate to get around a house and climb slightly to a road. Follow the road down to the left and reach a footbridge near the Moulin des Rochopts.
'' Yellow markings'’ (very infrequent only apparent after a few hundred metres)
(9) Take the bridge and admire the mill on the right. After the bridge, turn right onto a gravel road along the river to the right. Pass a small road coming from the left and a launching area for boats on the right and continue along the river (note on the opposite bank there are some nice big houses).
(10) At a lawn with buildings in the distance on the left just after passing under a power line, leave the gravel road and turn left, going straight along a path still keeping close to the river. Finally reach a tarmac path at a high voltage pylon near a major road on the left. Cross that alley and find a marker post on the left.
’’Yellow Markings'’ ‘’(reasonably dense)’’
(11) Continue opposite in the direction of "Brunoy Centre" then immediately turn right on a bridge over a stream (washhouse onthe right). At the end of the bridge, turn left into the woods. At a kayak club building, make a right-left dog-leg then move away from the path to reach the right bank of the Yerres (do not cross the river) and note two menhirs with their "feet in the water” on the opposite bank. Return to the path and continue to the west. Then pass over a (masonry) footbridge on the right and then a small bridge located on the east end of the island from the start of the hike. Go under the railway bridge.
‘’No markings (except at the very beginning where there are still some Yellow markings)''
(3) Unless you want to see the menhir of La Pierre Fritte and the Saint-Médard church, not to resume the route taken on the on the outbound leg on the left, but continue opposite on a wide concrete alley. Take the first bridge on the right to cross the river and leave the Yellow markings. Climb across a street with car park on the right. At the top of the hill, turn left towards the theatre and then right at the corner of the garage to quickly arrive at the Brunoy train station.