Head to Igny (Essonne) by train on RER line C. From the station, to reach the GR11 you have to cross the village, pass through the church square, the "only" café-tobacconist, the bakery, then turn right (Rue du Moulin), pass the railway line as far as the bridge, turn left just before the bridge and follow the river (you are now on the route of the GR11).
At the outskirts of Igny follow the GR11 along the Bièvre. Cross a small road, again follow the Bièvre and then a pond. At the end of the path on the road (1), go under the bridge and take the road immediately right at the foot of the bridge, then immediately left.
(2) Follow Rue des Prés and Chemin des Prés de Vauboyen along the railway line.
Arrive at the Vauboyen train station (3), head up to the right. At the junction, turn left and then immediately right into a street that turns into a path. In the forest, turn left heading downhill and after two left-right turns, reach a road (Rue de la Manufacture des Toiles de Jouy, fence). Take the road on the right and walk along the INRA Centre (fence and wall on the left).
(4) Take Rue du Montcel right then left onto Rue de Beuvron for a few metres and then finally turn right (you will walk by some beautiful buildings).
(5) Take the path on the right (nice little hill) and along a staircase that will leave a good memory. Turn left, follow Rue Pierre Vaudenay then Chemin du Cordon.
(6) Take a left there and walk through the woods. (7) Turn left and then right, and reach a road. Cross the road and go under the bridge and the Petit-Jouy-les-Loges train station. Take a path to the right along the Bièvre. At a stud (8) turn right, cross the road and take the path that climbs through the forest.
There is just 5 km left, keep it up. Follow the GR11 in the forest. (9) Head down a good stretch of hill (quite slippery in the rain). At the end of the road you will be at the sign for Versailles. Pass under the bridge.
(10) Take the path to the left (picture Versailles 1). After the National Forestry Office, head over the railway bridge, follow Rue Édouard Charton up Avenue de Sceaux.
Turn left onto this avenue, the castle is at the end of this avenue on your right.
You can see it!
To get back to the RER C you can just go down Avenue Sceaux for 300 m, turn left on Avenue de l'Europe (the station is 100 m further on).
