(S/E) Departure from Col de Grenouze (in the commune of Longes 69420), where you can leave your vehicles in the car park.
Head towards Col de Pavezin (signposted by the Parc du Pilat markers).
(1) When you reach Col de Pavezin, take the small path near the large Pilat Park sign in the large car park (do not take the path at the back of the car park).
There is a short, very steep climb through the woods to reach a forest path. Follow the path, walk along a short stretch of road for 50 metres, then take the path on the left to pass above the Grange Rouet inn. Continue to the Croix de Montvieux, pass the two restaurants, turn right towards the Croix du Mazet, and be sure to follow the IGN map carefully (the paths are not always marked).
(2) When you reach Croix du Mazet, cross the road and head towards Croix du Cerisier.
(3) At the cross, take the small path on the right towards a place called Seyoux. In the hamlet of Seyoux, head towards Sainte Croix en Jarez and, just as you leave, take a small dirt and grass path on the left that goes downhill, following the wooden sign for Les barrages de Couzon. You will then arrive at the stream that feeds the small dam.
(4) Walk along the small dam until you reach the small retaining wall of the large dam. Walk along the large dam, either on the left or on the right (more enjoyable).
When you reach the large retaining wall of the large dam, walk along the Maison du Barrage to climb up to the Marlin rock. After the house, take the small path, go up and take the path that climbs up again to the right, even though it is blocked just after the sign indicating the "Tourettes et des roches de Marlin" route. Twice you will find agricultural gates that are easy to open to walk along the cereal fields. Remember to close the gates behind you!
(5) It's a good climb, but the view from the top is sublime. Continue along the ridges of the Roches de Marlin to reach the Croix de parish specific to Brittany, take the path towards the hamlet of La Garde, then towards the Château in the commune of Longes.
(6) Take the long, fairly steep climb towards the Croix de Longes, then follow the Pilat signs indicating the direction of the Col de Grenouze, your starting point (S/E).
Very well marked, few roads, the trails are very pleasant. I recommend it.