How to find it
The quickest way is to drive up the track which leads off the D217 opposite the track to Aven de la Forestiere, passing the dolmen and then continuing to the junction with the GR4 (near spot height 397 on the IGN map). However, in 2005 this track was found to be obstructed by an earth barrier near the D217; this would be passable in a 4x4 but not in a car. Instead, drive further south along the D217 to Orgnac l'Aven and then follow the D174 towards la Garn. Just before the spot height 278 on the IGN map, take the road to the left until a crossroads (just after a vineyard on the left) where you turn right. Follow this until a road leads off to the left marked K17. Follow this (past a fenced compound to the left), passing a branch off to the right, until it becomes a rough, stony track and persevere for some distance until a junction. Turn left and continue to a junction of tracks with two signs marked "Chasse Gardé". The track ahead and slightly to the left (looks like straight on) is the route leading back to the D217 described above. Take the track at half-right and continue, passing another on the left, until a point where a track(*) splits off to the right. Park just on the left here (WGS84 datum, UTM grid: 0615941 4909917). Very shortly further on, there is another track to the right which joins up with the track marked (*). To find the cave, follow this track until it arrives at an open area with a tree in the centre and a ruined stone hut at the far side. To the right, a further track leads off. Follow this until it reduces in size to a small path. After some time, the path turns to the right, descending gradually. Some distance after this a point is reached where a moderately obvious right-turn leads almost immediately to the hole. Cave coordinates: 0616215 4910417.
Allow one hour's driving time from Vallon-Pont d'Arc to the cave if taking the route via Le Garn.
Both routes are accessible and equally horrible (car with some clearence is needed). The remains of the mound are in place but are not obstructing the road. RG4 road is well travelled and much better Laval-St-Roman NS route could be used to reach it if (no tarmac but nicely flat).
A fine pot which is equipped with fixed hangers throughout. An initial Y-hang from two such hangers leads to a rebelay from a tree; shortly afterwards, a deviation from one of two fixed hangers on the other side of the shaft provides a clear hang to the bottom. The view whilst descending, with light filtering in through the various orifices, is very impressive.
A bolt on the right-hand side of the gully provides a rebelay, succeeded by another on the left-hand wall a short distance further down. At the ledge, a Y-hang on the right-hand wall provides the belay for the next pitch, which drops quickly to a rebelay from one of a pair of hangers. The base of the pitch is a large ledge, where climbing up on the right leads to a further hanger on the wall and then a Y-hang. Ninety metres of rope suffice to the first bolt of this Y-hang.
The pitch descends to a sloping ledge, where a bolt on the right wall leads to a Y-hang. Forty metres of rope is adequate up to here; thirty-five metres are required for the following. From the Y-hang, the pitch descends to a rebelay and then reaches another sloping floor, at the end of which is a bolt for the final very short drop onto the top of a large slope of choss.
Descending the choss slope with care leads to a fine array of columns and a grotto. Beyond this are two small crawls leading to chambers. The left-hand one closes down; the right-hand one terminates at an exposed climb which looks tricky (spits in place for a rope).
No carbon dioxide problems encountered around Easter 2001 and 2005.