1
From the "Porte d'Herbouilly" car park (alt. 1280 m), descend along the road towards St-Martin-en-Vercors. At the "Carrefour des Vialarets" (alt. 1185 m), take the forest track on the left, following the yellow and green markings.
2
Continue along this wide track through the undergrowth to the "Noeud de Parcelles" (alt. 1240 m). Continue straight ahead to reach "Le Grand Bois" (alt. 1280 m), then leave the main track to find a path on the left towards the Grotte de l'Ours.
3
Climb this pleasant and bucolic single track. Ignore a trail to the left towards the Col de la Sarna, and follow the path to finish the climb on the slope which has become steeper and rejoin the trail at the "Grotte de L'Ours" (alt. 1370 m), for a welcome break.
4
Take this trail again to reach the "Col de la Sarna" (alt. 1395 m), gateway to the Vercors High Plateaux Nature Reserve. From there, the bravest can continue to the Darbounouse Plain, to enjoy magnificent landscapes, characteristic of the Vercors high plateaus (allow 45 minutes return to enjoy a clear view, and at least 1 hour 30 minutes return to reach the GR).
5
At the Col de la Sarna, follow the signs for La Royale. At the first intersection, turn right, then further on, at the T-junction, go down the track to the left.
6
At the "Carrefour de la Royale" (alt. 1355 m, entrance to the reserve), continue straight ahead, pass through the barrier. Walk for a long time on this wide track without paying attention to the secondary paths.
7
Pass the “Dodos” crossroads (alt. 1305 m), then the “Pot de l'Aygue” crossroads (alt. 1300 m).
8
Go to the “Carrefour de Roybon” (alt. 1305 m), then the “Auberge de Roybon” (alt. 1300 m) and finally the Porte d'Herbouilly car park.
