I almost founded it.
Located in the Vercors mountain chain (Alps), this spot is a cliff ending a deep valley facing noth wind. the edge est 300 m large and the start of a huge flat field, perfect for landing.
The parking is close to the slope, there is no walk to do.
On the following panoramic picture, you can see the deep valey on the left and the "wall" on the right :
but unfortunately, there is a "hic", in fact a double problem. First of all the owner forbids slope soaring here, and second there is trees and bushes on the edge that prevent to install an F3F course with buzzer men and DC, launch the plane, have a good visibility.
This is really a shame because for the rest, it's perfect !