How to find it
Take the C6 road (marked on the map as the D690) eastwards from its junction with the D290 (the main Ardèche gorge road). After a while there is a hairpin bend followed by a straight section. Just after the straight section the road bends to the left and an open stony area opens on the right. Towards the left of this area, a track leads off into the woods. Follow this past a junction with another, grassier track which joins from the left, until a fork is reached. Take the good track to the right and follow it until it ends at an open area of limestone; the entrance is a manhole in the obvious concreted area.
On the IGN sheet 2939OT, the track to the hole is marked but the hole itself is not.
Grotte de St. Marcel
Following the D290 eastwards from the junction mentioned above, the road bends left at the Grand Belvédère and then around to the right again. Just after the latter bend, take the track (which also heads to the Les Grottes campsite) which leads off to the right and descends via a series of hairpins. After a while there is an area on the right where you can park and just afterwards a track leads down from the left of the road. Following this quickly leads around to the entrance which is on the left.
The cave is marked on the IGN sheet 2939OT.
Use the link on the Aven de Noel page to obtain permission and a key to the bottom entrance.
Aven Déspeysse to St. Marcel through trip
A long and superb trip -- allow ten hours and be sure to take copies of the surveys (see below for links). Look out for (often large) carbide marks on the wall marking the way to various sections (N1 etc.). From the top entrance downwards, there was a detectable draught blowing upwards in early April which provided a good aid to route-finding. The majority of the navigation is easy, but care needs to be taken in certain areas as noted below. If doing this for the first time (particularly as an exchange trip), be aware that it is easier to navigate from the top downwards.
The following description is only an outline, but should suffice to get you from top to bottom coupled with the surveys.
If attempting the through-trip, it is necessary to first go into the bottom entrance to open the gate in the window ("lucarne") which leads from this section of the system into Réseau 2 (from where one will emerge coming from the top entrance). Dry grots will do for this job, which shouldn't take more than half an hour or so. Enter through the gate at the bottom entrance and follow the large passage, up the fixed ladder and beyond, into the large Cathédrale chamber. One should keep quiet in here if the showcave is in operation (which will be obvious by the presence or absence of a son-et-lumière show; the whole chamber may indeed suddenly be illuminated!). To find the gate, follow the big power cable almost to the bottom of a fine white calcite slope which it ascends. The gate is slightly lower than the bottom of this and to the right as you look at the slope. Having opened the gate, proceed back to the bottom entrance and then drive up to the Déspeysse entrance.
For Déspeysse, see rigging guide below to arrive at a traverse heading off. Follow this for a good way; there are several traverses, ascents and descents which are all rigged on fixed ropes. Eventually ropes lead down a large slope; at the bottom there is a smaller passage to the right, and a more obvious intersection with a large passage at a junction where there is a prominent stal which looks rather like a chilli pepper hanging from the roof, with a boss underneath.
Turn right and follow the main passage to reach a traverse on the left wall around a large hole. Continue in the obvious passage at the same level as the traverse to reach a big stal boss on the right, with well-travelled mud slope ascending. Straight on here is N10. Turning right up the slope, large passage continues to another traverse, further passage and then a traverse where the passage continuing doubles back under. Not far afterwards N9 is passed on the left. Continue to reach a large gravel slope: climb to the top and then traverse around to the left, reaching more large passage. After a while you traverse around a lake, and then pass N7 on the left. Continue until you reach a T-junction, with N6 on the right. Turn left here and follow the main passage which enlarges. Some large columns are passed before a gour pool is reached blocking the way; a small passage on the right of this continues to the other side of the blockage. Continue down the passage for some way, passing gour pools and then eventually a small lake.
Keep a lookout on the left for "N1" written on the wall in large black letters. At this point, continue in the main passage further, and watch carefully for a low passage on the left after a while (marked "N0" I think). Crawl through the low part, and follow it around to the right to drop into a small chamber where you continue to the right. Follow the main passage down (passing a stal inscribed with an arrow and "N1" pointing back from where you've come) until it degenerates into a crawly section. This continues for some time, including a short unpleasant section over sharp gours, to eventually enlarge. A junction is reached with a wide, but not very high, passage to the left; half left is a further passage; and straight ahead is a third passage. The passage to the left is marked "F".
Take the half left passage, which continues for some time until a (slightly unobvious) junction where you must turn left, under some stals, into a continuation of the passage. According to the survey, continuing along the main passage here quickly leads to a sump. Continue onwards through tedious stooping passage, passing some pools, to eventually emerge in a larger chamber where you turn left. Continue further to reach a chamber marked "A" on the wall. From here, a slightly awkward, but short, section crawling over sloping flowstone emerges in good-sized passage, with increased draught and a white channel in the floor (maybe carries a stream sometimes?). Follow this, keeping to the left (and passing the smaller passage leading to Réseau 3 on the right). A smaller passage, with a brief crawl, leads to some climbs through calcite and then a handline drop into a pool. The passage continues, passing through an area of stals, to the short climb up and through the gate. Exiting through the window brings one to the Cathédrale chamber.
Follow the direction in which you look out of the window to reach large passage. This continues for some way, via a fixed ladder pitch in the middle, to eventually arrive at the bottom (St. Marcel) entrance.
No equipment is in place for pull-through, which would be foolhardy in any case unless completely sure of the route through the unobvious part (from the N1 junction until the junction with Réseau 3).
In flood conditions, at least the second pitch is dangerous.
First pitch (9m): Backup to ring in manhole lid, followed by further backup from bolt on right wall and then two bolts at pitchhead. Rope protector useful half-way down. 25m rope, 1 sling+krab, 3 hangers+maillons.
Second pitch (22m): At the end of the crawl, backup from two threads followed by Y-hang on the left just at the pitchhead. On the right-hand wall at about the same level at the Y-hang (and further out) is a thread which provides a deviation almost immediately. This rigging provides a somewhat unlikely free-hang to the bottom of the pitch, the bottom half of which is more of a climb in places. 9mm rope probably not advisable as the Y-hang isn't in an ideal position! 35m rope, 3 slings+krabs, 2 hangers+maillons.
Third pitch (7m): From the bottom of the second pitch, a short climb down followed by a squeeze over a puddle leads to a small chamber. Climb through the hole in the wall (sounds as if it emerges over a pitch but it doesn't!) to reach a large ledge. On the left, a bolt provides a backup for a hang from a large stal boss on the left, leading to a descent over flowstone. Continue rope to next pitch.
Fourth pitch (28m): At the landing of the third pitch, a Y-hang backup is followed by two spits at the pitchhead (two figure-8s preferable rather than a Y-hang). Descend over flowstone to a deviation bolt on the far wall just above the main drop. This is followed by two further deviations, one about halfway down and one a few metres above the floor. A Y-hang at the landing provides the belay for a descent down the gours to reach a pool and passage leading off around to the left at the bottom to reach the next pitch. 80m rope (can be joined to next rope at first bolt of fifth pitch as an extra backup), 10 hangers+maillons, 6 slings+krabs.
Fifth pitch (15m): Stoop through the flowstone to reach two bolts in the ceiling and to the right. Descend to single rebelay bolt on right wall. The aim is to get to the window on the other side of the shaft; this is a long way across and the easiest way is to descend all the way to the pool at the bottom and then bridge up in the obvious chimney. Having gained the window, a rebelay Y-hang in the roof (producing a pendule for the previous section) followed by a short descent leads to the start of a traverse leading off. There is a further hole in the floor here which is the wrong way! 30m rope, 5 hangers+maillons.
Total gear used: 25m+35m+110m rope, 10 slings+krabs, 20 hangers+maillons.
Bottom of the fifth pitch to the St. Marcel entrance
There are lots of traverses, short ascents and descents, all of which are rigged. No further gear except that above need be carried.
These can be found on this website (use the rigging guide on this page though!)