How to find it
Continue past parking spot for Aven Richard (going away from Marzal showcave); on a bend to the left there is a sign (advertising another cave, the Madeleine I think). Immediately at the bend a forest track goes off to the right. You can drive up this for some way until you meet a forest track sign pointing three ways. Either park here, or keep driving straight (a little narrow through the trees) until the track becomes less rough. A short way on, a path goes off to the right (at about 2 o'clock) and you can park here. Continue up the main track, past a piece of wood marking "22" on a tree on the left, and go past two paths on the left (one shortly after the other). The second path has a stone wall on the corner of the turning. Shortly after this, there is a break in the stone wall on the left (unobvious). Walk into here and follow the small track to arrive at the hole. If (on the main track) you reach a larger turning on the left marked "23" you've gone too far.
Very big pitch: see Speleo Sportive en Ardèche. A pair of strong underpants may be useful.
Watch out for carbon dioxide: there are reports of reaching the gas only one-third of the way down.