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Park in the town hall car park at Congis-sur-Thérouanne (12km north-east of Meaux and 18km north-west of La-Ferté-sous-Jouarre).
Unmarked
(S/E) From the town hall car park, take the road on your left (Rue de la Poste). Immediately cross a river (the Thérouanne) and head towards the church.
(1) At the church, turn left onto the D121E towards Isles-les-Meldeuses. After about 100 metres, at a fork in the road, leave the D121E and turn right towards Montier. After another hundred metres, at another fork, turn left (south) onto Chemin de l'Epine Blanche.
(2) Just after passing a large white hangar on the right of the road, look out for a black gate on the left: a few dozen metres past this gate, take a passageway that leads into the nature reserve (information panel). Descend briefly in a right-left zigzag, leaving a "Domaine du Grand Voyeux" sign on your right, and head towards a blue "Protected species refuge area" sign at the foot of a pine tree.
Follow the path (not shown on the map) eastwards through the pines and then the birch trees. At a T-junction, turn right towards a barrier behind which you can see a pond. At the gate, turn left onto a wide path between the trees (the pond is still visible on your right). You will come to a sort of grassy roundabout with an observation post on the right: don't hesitate to spend some time there.
(3) From the observation post, continue east along the wide track, which soon opens out into a meadow on your right. The path bends to the right, with the meadow still on your right. You will come to an open space (fence on the right). Turn left at a right angle and walk along a pond on your right. Go through a metal barrier and emerge onto the D121E road.
Red and white signs
(4) Cross the road and continue straight ahead towards the Villers-lès-Rigault power plant (sign). When you reach the entrance to this very large building (sign), turn left at a right angle onto a path lined with plane trees. Cross two perpendicular streets, go to the end of the path towards a small white building and emerge onto the Canal de l'Ourcq.
Yellow markings
Let the GR® go right and turn left onto the towpath, with the canal on your right.
(5) Just after passing the Pont des Carreaux, at a fork, take the right-hand lane and stay along the canal. Just before the next bridge, leave the towpath (which passes under the bridge) and take a steep left to join the D121E road (see a variant in the practical information section).
Red and white markings
(6) Cross the canal and immediately turn left towards the canal. After a few metres, at a fork, do not go back to the canal bank but take the path on the right that enters a wood. The path bends to the right and joins the River Thérouanne (on your left). Continue along the edge of a wood (poplars on your left) and a cultivated field (on your right).
(7) After a long straight stretch, leave the boundary path and turn left at a right angle to enter the wood and join the Thérouanne. At a T-junction, turn left, cross the river and climb slightly towards a bridge over the Canal de la Thérouanne.
Yellow markings
(8) Do not cross the bridge but turn right onto the towpath. Follow the canal on your left for approximately 1.8km. At a bend, find the river below on the right and note a football stadium on the opposite bank (how many balls have been lost in the water?) At the end of a straight stretch, reach a bridge, with a gate on the right and a barrier and gate system opposite.
(9) Turn left at a right angle and cross the canal (information panel on the right). Go up the track opposite to a small road. Turn right onto the road (on the right is a beautiful view of the Château du Gué). Find the river below on the right and note the buildings of a technical college on the opposite bank.
(10) Before entering the hamlet (house with red-tiled roof), leave the road and take a path that climbs to the left between two cultivated fields. Shortly after the top of the hill, ignore a perpendicular track on the left (which leads into a field). A few metres further on, just as the main path seems to get lost in the field on the right, veer left onto a path that starts between two trees, each bearing a yellow marker. The path descends steeply and leads about ten metres above the Canal de l'Ourcq.
(11) Turn right at a sharp angle. Stay on the path for a good kilometre as it winds through the undergrowth, still high above the canal (on your left). Go past the canal weir on the opposite bank (marked "vanne" on the IGN map), which can be identified by the sound of a waterfall. At a fork in the road, take the left-hand lane and go downhill for a few metres. Turn right onto a path with wooden steps that leads down to the entrance of a tunnel under the canal.
(12) At the bottom of the descent, turn left and enter the tunnel, which has a paved floor. There is usually water flowing or trickling down, so keep to the sides, literally "keeping your head above the water". On leaving the tunnel, cross two metal bars and come out on the edge of the D121. Immediately turn left onto a path that leads up to the edge of the canal. Follow the towpath to the right (north-east) and reach the weir. Continue along the canal for approximately 900m.
(13) After a small house with a zinc roof on the right, look out for a path on the right (yellow arrow). Ifyou see a "Congis-sur-Thérouanne" sign on the opposite bank, turn back. Leave the towpath and take the path. Cross the D121 (take care) at a slight angle to the left. Take the path that goes off to the right at an acute angle and runs alongside a wall on your right. Bend left and head south-west between two hedges of trees. Reach the right bank of the Marne at Port la Pierre.
(14) Turn left and head upstream along the Marne, which is on your right. After approximately 200m, the path bends left to run alongside the right-hand bank of the Marne, alongside Ile de l'Ancre. Cross the Thérouanne just before its mouth. Bend left and move away from the edge of the Marne. Make a left-right zigzag and emerge onto a wider track at a place called La Gueule du Ru.
(15) Turn left at right-angles onto a track between cultivated fields. The track bends right twice and comes out into a street (Rue des Grands Prés). Pass Rue de la Marne coming from the right and enter Rue de la Pierre Lorraine. Turn left into this street. At the stop sign opposite the church, turn slightly left into rue de la Poste.
(1) Go past the church, cross the Thérouanne one last time and return to the town hall car park (S/E).
Visorando member
Difficult 
Association / Club / Walk leader
