Cascade de la Gueule d’enfer is an unknown waterfall with a single drop of 80 meter, located along road N102 at Thueyts in the Ardeche, France.
I am not sure where you have a good view on Cascade de la Gueule d’enfer. When driving on road N102 there is a big sign with « pont du Diable ». Park the car here (gps 44.675310, 4.223773).
Probably when you walk to the viewpoint on the bridge you should see the waterfall beneath the bridge. Another option is to go back to the car and drive east for 1 kilometer, in the direction of Aubenas, until there is a small sign (pointing right) « viewpoint pont du Diable ». Drive down the road for again 1 kilometer until you are driving over the river again. Maybe the view over here is better.
Unfortunately there ain’t much other information available about Cascade de la Gueule d’enfer. I think it is a waterfall that doesn’t flow all year around.