Departure from Pelussin. Ask if you have never been to the village before. The viaducts are well known (former railway line). Park in the pharmacy car park.
(S/E) Take Rue de Verdun and leave it by turning left towards the viaducts.
(1) Just after the second viaduct, turn right onto the tarmac road that joins the Maclas departmental road (D19). Follow it to the left (due south) for about 300m (watch out for cars).
(2) You will then come to a very wide path coming from the left (at a cross): take the tarmac road that climbs up to the right, directly opposite (due west). Climb for about 300m and pass a stone house on the left.
Just after the house, take the beautiful wide path that branches off to the left, follow it for about 300m, then turn right onto a stony path that climbs, wide at first but becoming narrower (and steeper). Climb for about 10 minutes through this wood. Nice trail in the undergrowth.
At the exit of the Valette woods (the path becomes flat), you will come to a path that you follow to the left to reach a crossroads.
(3) At the Regional Park signposts (directions and altitudes), turn right onto the path that climbs towards Chavardet. After 500 metres, the path crosses a fairly open field and joins a tarmac road. Follow it to the left for 150 metres to reach a crossroads.
(4) Continue straight ahead on Route des Plâtres towards the Chavardet farm. The road then passes 20 metres below the farm.
(5) 200 metres after passing the farm, find the path on the right that enters the woods (signposted "propriété interdite" [no trespassing], actually intended for motorised vehicles). The slope is quite steep and there are a few hairpin bends. Continue through the undergrowth until you pass under a small fir tree plantation and exit the woods at the junction of a path.
Take this path on the left and tackle a fairly steep climb straight ahead (landmark: after 300m, under the fir trees, you will come to a clearing). Continue straight ahead. The space opens up and you will reach the forest road used by mountain bikers.
(6) At the junction, follow the track for about 500m.
(7) Take the path on the left (towards the Rocher de Dentillon hut). Cross the arboretum (tree species indicated by small signs) and climb towards the hut. Once you reach the Dentillon hut (altitude 995m), there is an orientation table and views of the Alps (Mont Blanc, Belledonne, Meije, etc.) and the Pre-Alps (Vercors, Diois, Trois Becs).
(8) Return via the same route to the car park (S/E).

