This is a short hike from Le Gua, between Planfay and Proveysieux in the Chartreuse up to the ridge known as the Rocher d’Église. You start at Pont du Gua at 640m, where there is roadside parking for perhaps 3 cars, and climb unrelentingly up to the Petite Sappey Cabin at 1140m. I say unrelentingly because it is a punishing continuous uphill climb with no horizontal sections. This isn’t undulating - it’s just up! It isn’t that long - being only around a 5km round trip.
Once you get to the cabin, there are 2 paths that continue to the North East or South West - but they don’t seem to go anywhere. They’ll get you a little higher up the ridge, but not to the top. That said, the ridge is only around 200m from the cabin - and the incline at this point isn’t steep - so it’s quite possible to make it up to the tiny path that runs along the top of the ridge.
I took the NE path, and went up to the spot I’ve marked Viewpoint on the KML file. This is a good spot for lunch, at 1308m