Cascade en Gouffre d’Enfer is a waterfall in a canyon north of Planfoy not far from Saint Etienne, in the region Loire/Rhône-Alpes, France.
In St Etienne take exit 23 and go right to “Gouffre d’Enfer”. Follow the road and keep following the signs “Gouffre d’Enfer” for 8 kilometer. There is a parking at the Via Ferrata (gps 45.395150, 4.448447).
From the parking follow the road further west and within a few minutes you should see Cascade en Gouffre d’Enfer. The waterfall is situated in a gorge north of the dam Barrage du Gouffre d’Enfer and is often used for canyoning.
As far I can see is the flow of the river fed by water from the reservoir above. I am not sure if the river flows all year around and if it is accessible by foot without canyoning.