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The hike starts at the car park in the hamlet of Mongrésin, in the commune of Orry-la-Ville (Oise). This hamlet is located on the D924a south of Chantilly.
(S) Start by following the D924a towards Chantilly. Turn right as you leave the hamlet onto the track between the school and a red brick shelter. Follow this track along the fences and, at the next crossroads, take the path to the left of the gate to a large meadow.
After 200 metres, turn left, leaving theGR®1(red and white) marked trail, which continues straight ahead. After 500 metres, you will arrive at the Saint-Hubert post in the middle of a crossroads.
(1) Turn left onto the Première Route Ronde towards the Croix de Mongrésin. Cross the D924a and continue straight ahead on thePR® (yellow) marked path, leaving a path closed by a barrier markedGR® (red and white) on your left. Continue to the next crossroads, where thePR® turns left.
Turn right and continue for 500 metres to the crossroads near the Table de Mongrésin rest area.
(2) Take the small road on the left. This crosses another road a little further on. At the crossroads, continue straight ahead on the path that leads into the vegetation after passing between two small posts markedPR® Yellow.
The path is straight for about 2 km. Along this section, you will walk alongside forest plots, the numbers of which can be seen from time to time (notably: 318, 319, 341, 342, 344, 324). Continue to the large crossroads at the corner of plot 347 (this is the Abreuvoir crossroads, but there is no signpost).
(3) Turn onto the Abreuvoir forest road (2nd on the left). This road leads to a crossroads with a tarmac road running alongside the Etangs de Commelles ponds below. Cross this road and go down to the edge of the pond using the path in front of you to enjoy the beautiful view of the Château de la Reine Blanche.
(4) Then go back up to the crossroads and turn left onto the forest road, which is closed to motor traffic (except for authorised vehicles).
This straight road leads you to the railway line, which you cross by passing underneath it. The path turns right and then, after about 50 metres, left. At the fork that follows immediately, keep to the right.
You are now on a bridle path that is quite busy in the morning, so be careful. It curves to the right, climbing up to a crossroads a few hundred metres further on. Cross it and continue straight ahead to a fork where the bridle path turns right. Continue straight ahead.
(5) You will pass in front of the Red Cross Training Institute. At the crossroads at the end of the estate, take the bridle path straight ahead, which descends. At the hairpin bend to the left, cross the safety barrier for horses and continue straight ahead along the path between two wire fences. It ends at Avenue Jacqueline Mallet at the junction with the D1016.
(6) Cross the D1016 and make a zigzag right-left to enter Lamorlaye via Avenue des Merisiers. At the crossroads, turn right into Rue du Beau Larris, then left at the roundabout into Avenue Plein Soleil. At the end of this road, turn left and then immediately right to follow the 2nd Avenue.
(7) Cross the Rond-Point de l'Etoile roundabout and continue diagonally left along the 1ère Avenue (4th on the left), which ends in a cul-de-sac for vehicles but remains accessible to pedestrians.
At the junction with Avenue Charles de Gaulle, continue straight ahead along Chaussée de Bertinval. You will cross Ru Saint-Martin and Vieille Thève in succession to arrive at a commercial and craft area. Cross the large roundabout to pass between two commercial buildings and reach Nouvelle Thève, which you will cross. Continue straight ahead on the path that climbs into the forest, following forest plot 434.
(8) When you reach the plateau, at the Bertinval signpost, turn left onto the Royaumont road towards the Lamorlaye crossroads.
At the Lamorlaye crossroads (junction with the D1016 at the corner of plot 478), cross the road and continue slightly diagonally to the right.
After about 1.5 km of straight road, you will arrive at the corner of plot 469, a few metres from the edge of the forest. Turn left and go through the barrier to enter the village.
(9) Continue straight on along Avenue du Bois where, a hundred metres further on at Rue de l'Orée du Bois, you will find the first sign indicating the name of this avenue. At the roundabout, take Rue du Layon de l'Enclave, the second street on the right, which will take you back into the forest.
(10) After a few hundred metres, turn left in front of the gate to a property. The path first curves sharply to the right before curving to the left and climbing up to a crossroads in a clearing. Turn left to cross the road and take Chemin du Crochet de Coye.
(11) About 50 metres further on, at the corner of a wire fence, turn right onto the path that leads into the forest. It runs alongside this wire fence with a row of houses and ends on a forest road near a railway bridge.
Go under the bridge and continue along the forest road, veering slightly to the right. The road curves to the right and, at the next junction, meets another road markedGR® (red and white). Turn left to go to the Grandes Ventes signpost, where theGR® turns left.
(12) Continue straight ahead to the edge of one of the Etangs de Commelles (the Etang Chapron) after crossing the Alix crossroads.
(13) Turn right to follow the path along the water's edge, which has been turned into a botanical trail where you can see educational panels about the flora of the area. Continue to the boundary wall of a property. Turn left, cross the Thève and climb the embankment in front of you to reach a small tarmac road where you turn right.
(14) Turn left at the crossroads; this road will take you back to the hamlet of Mongrésin. At the junction with the D924a, turn right to return to the car park where you started.
The hike is now complete.
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Hikers planning to do this hike, beware! 
This is what your terrain will look like:
quite an easy hike. Very pleasant. Next time, I'll cut across just before entering Mongresin to avoid going through Orry (walking on tarmac isn't parish specific to Brittany)
Visorando member
Moderate 
Easy 
Very difficult 
