The Saclay plateau and the woods and marshland of the Bonnard Valley

Start and finish behind the town hall in Saint-Aubin. Parking nearby.

(S/E) Take the path running alongside the community hall, then turn left onto a cross-country path (Chemin des Pommiers) and follow it to the edge of the Bois de la Guyonnerie.

(1) Turn right, then a few metres further on, left, and take the path “CR5 Chemin de la Fontaine Billehou”. At the start, this runs alongside the Rigole de Saint-Aubin, then descends into the woods along a fence. Arrive at Place de la Fontaine Billehou.

(2) Take the path that starts behind the sign for “Chemin des sciences et des traditions”. Follow this path and cross the bridges over the Marais Bonnard. At the edge of the marsh, cross a road, climb the steps and walk through the hamlet of La Petite Barrerie.

(3) At the end of the hamlet, at the sign for “Forêt Départementale de la Tête Ronde”, turn right onto Chemin de la Châtaigneraie, then opposite, onto Chemin de la Tête Ronde. Follow this path almost to the end.

(4) Turn left and a few metres further on, at the sign for “Chemin des Merisiers”, take a small path on the right which crosses a drainage channel and leads into a housing estate. After crossing a footbridge, take a footpath on the left which starts behind a gate. Follow it straight on, cross a road and you’ll come out at the Villiers allotments.

(5) Follow the path between the allotments and the ditch, then continue along the path that runs alongside the Rigole de Châteaufort. Take the path above the ditch culvert, continue straight on along this lane which crosses the village and leads to the Place de la Mairie. Continue straight on.

(6) At the end of the square, take the path that runs alongside the ditch and the Route de Saint-Aubin. Continue until you cross the Rigole de Saint-Aubin.

(7) Leave the canal on your right and continue straight on to the Saint-Aubin Town Hall (S/E).

During the walk, you can spot, along the channels, the Fleur-de-Lys markers installed when the network of channels on the Saclay plateau was created in the 17th century to supply the Palace of Versailles. On the road between Villiers and Saint-Aubin, at the “Biches” reservoir, into which the Châteaufort and Saint-Aubin channels flow, you can see the entrance to the Aqueduc des Mineurs, which runs underground to join the Saclay Ponds.

The Bonnard Valley marshland is a listed site and is rich in flora and fauna.

At the Place de la Mairie in Villiers-le-Bâcle, you can take a detour around the Vandamme farm to the church of Villiers-le-Bâcle.