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Park in a small car park at the end of Chemin de la Marinière (3 to 4 spaces plus around ten spaces in the street).
N.B. The map background chosen is OSM Trails because it shows several paths that do not appear on the IGN map.
(S/E) From the car park, head west-northwest and follow the path until you reach a junction with Chemin des Carriers (signposted).
(1) Take a path opposite (facing east), at the level of a dead tree. A little further on, you will reach the old Batterie du Terrier. Go around it on the right, following the ditch. After about 200m, you will come to a crossroads of paths. Turn right and go slightly downhill into a small hollow (on the other side, the path plunges into the ditch to climb up to the top of the battery). Continue along this path, which turns slightly to the right and joins the Chemin des Carriers and theGR®655further on. Follow it to the left for a few metres, then turn immediately right downhill, following the GR®.
A short descent takes you to a pond and a small wooden footbridge (muddy area). Go around to the right (5 m further on) if there is too much mud before the footbridge. Continue to follow theGR® and climb up opposite. When you reach a flat area, leave the path (and theGR®) and head straight ahead (path at the beginning), slightly to the right (do not go towards the roundabout and the road on your left). Join a path just before starting to descend. At the bottom, follow the oldGR® trail: take the steps on your left, then the road to your left towards the roundabout.
(2) Just before you reach the roundabout, take the path on your right. The slope is steep and often muddy. Halfway down, you will come across a road (Route de Saint-Martin). Continue straight ahead on a path that crosses a large meadow (muddy at first). You will pass the viewpoint of the former Batterie de la Châtaigneraie (orientation table). The battery no longer exists.
(3) Continue straight ahead (west) along a slightly downhill path and join the gravel path (Route de Saint Martin). Follow it for a few metres to your left and, at the entrance to the forest, take a path not shown on the IGN map but called MudMax on OpenStreetMap. As its nickname suggests, this section can be very muddy with three deep puddles. Although it runs alongside the noisy A86 motorway, this path is very pleasant and popular with mountain bikers. The path is easy to follow despite its winding route. Stay parallel to the motorway.
At each junction with a path, continue straight ahead. First take the Route des Muguets, then the Route du Bois-Brûlé, then an unnamed path, then the Route de la Mare Chabot and finally the Route du Trou Morvan (no sign on this section). The trail then emerges into a deforested area and runs alongside a fence. The mud puddles in this area can be deep and remain for a long time. You will then reach the Carrefour des Quatre Arpents and a road open to traffic.
(4) Cross the Route de la Mare-à-Chalot (watch out for cars) and take the forest lane opposite called Route du Plessis Picquet (sign). There is a car park with around 20 spaces just after the crossroads. Go to the end of this road (roundabout) and take the path on your left closest to the motorway fence. You will be on the second part of the MudMax trail. As before, there are no navigation difficulties. The trail will cross several paths, but you just need to continue straight ahead each time.
As a reminder, the paths you will cross are, in order, Route Brigitte, Route de la Sygrie, Route de la Lionne and Chemin des Cavaliers (there are no signs on this section). Between Route de la Lionne and Chemin des Cavaliers, there is a straight section (about 200 metres). At the next junction (with Chemin des Cavaliers) (no sign), take this road to the left. If the path crosses a thicket and immediately turns right towards the motorway, you have missed Chemin des Cavaliers. Retrace your steps.
(5) At the next junction with the Route de la Boursidière (path, no sign), take this road to the right (north-west). Pass under the high-voltage power lines. At the next junction, turn left onto the Route de Saint-Cyr (no sign), which joins the Route de Verrières (tarmac) further on (no sign).
Please note that between points (6) and (8), the paths used are not shown on either the IGN map or the OSM map. However, they do exist; the route is based on my GPS track.
(6) Cross the road and continue opposite on the path that branches off to the right. The start of the path may be overgrown with brambles, especially in spring. Walking sticks may be useful to clear the way. At the end of a long, slightly downhill straight section, there is a left-hand bend.
(7) At the bend, the slope becomes steeper, so be careful not to slip. The path descends to a stream on the left. Continue along the stream and follow this path. After a short climb, the path goes around a housing estate (Le Bouquet de Chatenay) on the right. Just before reaching the paved road leading to this housing development, the path may be overgrown with brambles (Chemin de la Porte Jaune). Take the road on the left towards the forest, pass a ruined house and then the entrance to the housing development to reach the start of Route de la Sygrie (barrier, sign).
(8) Turn right onto a flat path running alongside the water treatment area below. A climb awaits you a little further on. At the start of this climb, leave the path and take a trail on your left. It climbs up a ridge, passing under the high-voltage power lines. At the ridge, take the path on the far right twice. The path then descends and joins the Chemin des Gardes at a crossroads and a building (graffiti wall). Continue along the Chemin des Gardes (flat) which runs alongside the wall (graffiti) at the beginning.
''N.B. June 2018: forestry work has made part of the route impassable. The route has therefore been changed."
At the next junction, continue straight ahead on a flat path. A little further on, this path crosses a small valley (downhill then uphill, short but steep) and joins another path 150 metres further on. Take this path uphill (left). You will come to a path (markedGR®) higher up, which you should take to the right, heading south. When you see a wide path descending to your right, follow it. At the bottom, you will come to another path, which you should take to the left.
(9) Be careful, this area can be tricky as there are many paths. Don't worry about the paths going uphill on your left. Continue straight ahead, slightly uphill. When your path begins to descend towards a gate (Chemin des Mulets) (no sign), immediately take the path on your left (going slightly uphill) which then runs alongside a fence and houses (tennis court below). If you reach the gate, retrace your steps for 30 metres; you have missed the path. The path is flat at first, then more hilly before arriving at a wall (with lots of graffiti). Continue along this path which runs alongside the wall. You will cross several paths on your left going up to the top of the forest. Stay on the path that runs alongside the wall.
When you see a path climbing up the slope in a nice curve to the left, take it. Climb for a good hundred metres until you see a path sloping slightly down to your right and take it. Be careful, this path is easy to miss. Pay close attention. After 50 metres, you will come to another valley (long descent, steep climb). Continue along this path. At the end, it splits in two. Take the right-hand path (with logs across it). A few metres further on, you will come to a junction with a path leading downhill, the Chemin de Vaudrot (no sign). Go down this path, which runs alongside a house, until you reach a road on your right (Allée du Bel Air, with a barrier).
(10) Take the path on the left (south), which continues along the road. A little further on, you will begin a descent to the lowest point of this tour. At the following crossroads, always take the path on the right. When you reach the Bièvres road (traffic), follow it, staying on the path above the road, to your left until you reach a picnic table. The Bièvres river flows nearby (about 50m below).
(11) Take the path opposite (closest to the road). When the path splits in two, take the right-hand path. Further up the hill, turn left at a wire fence. Then turn right (area with dead trees), then left (fallen tree) and finally right again just after that. A little further on, when the path climbs again, take the first path to the right. A slight descent across the path takes you to the junction with the Route de la Princesse (path) (no sign). Take the path on your right (uphill). Be careful, the Route de la Princesse also climbs but is further to the left and climbs more gently (at the bottom of the valley), do not take it. At the top, you will join theGR® (wide path called Route d'Amblainvilliers) (no sign), follow it for 50 m.
(12) At the end of the left-hand bend, take a small path on your right, then another one on the left 3/4m further on. Stay on this path, which remains level above the market garden plots. You will pass a small gully before joining another path that climbs uphill. Follow it for 50 metres. Then take the first path that descends slightly to your right and continue on the path at the same level, towards the left (if you have reached a clearing, you have gone a little too high, so take the path that descends to your right). Continue along this level path. You will cross paths that climb up to the top of the woods or descend; stay on your path, which remains halfway up.
At the end, you will face the toughest climb of the route to reach the BMX track. The start is easy (until you reach the pony club halfway up the slope) and the end is tough. Follow the BMX track on the left (path along the wall) and join the Route des Gatines (be careful of traffic) to return to the woods. After 20 metres, take the road on the right (Route de Montauzin) for about 150 metres.
(13) Take the path on your right closest to the road (on the left). This section can be very muddy. Be careful, as there are many mountain bikes on this trail. The path is well marked and runs along the edge of the forest plateau. Follow your instincts. Do not take any of the numerous paths leading downhill. Continue on this path until you reach the junction with Chemin des Violettes and Chemin des Carriers. You have finished and deserve a nice cup of tea or a cold beer.
(1) Turn right and follow the path you took on the way there down to the car park (S/E).
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