What to See Inside Aven Armand
The funicular descent, the Virgin Forest and the Grande Stalagmite — a concierge guide to the highlights of the guided Jules Verne tour.
Aven Armand is one chamber, seen on one guided route, which makes it unusually easy to prepare for: there are no wrong turnings and nothing to miss by choosing the other corridor. What there is instead is a single space 110 metres long and 45 metres to the vault, holding more than 400 stalagmites, the tallest of them around 30 metres. This guide covers the funicular descent, the dimensions worth fixing in your head before you go down, the Virgin Forest and its centrepiece, and — the part most visitors find they wanted afterwards — why these formations look unlike those in any other show cave.
What is the funicular descent like?
The visit begins with a funicular, and it is a genuinely unusual machine. It carries you 60 metres down in one minute thirty, inside a 208-metre tunnel cut on a gentle slope in 1926–27 — the tunnel the earliest visitors walked, 382 steps down and the same back up, until it was widened in 1963 to take a funicular. That first car ran on pneumatic tyres rather than steel wheels, a European first, chosen specifically so that noise and vibration would not damage the stalagmites below. It remains one of only nineteen funiculars in service in France and the only one in Lozère, and unusually it descends into the ground rather than climbing a slope.
The current car is the third generation. The « Aven Express » entered service on 4 April 2026, keeping the pneumatic-tyre principle and adding a multi-level braking system with overspeed detection. The tunnel is closed by doors at both ends, which is what holds the cave's microclimate steady at about 12°C and 90% humidity, and why the ride feels sealed rather than draughty. On the Jules Verne and Particulière visits the funicular is compulsory in both directions; on the Exploration visit you go down the 75-metre natural shaft on ropes instead and only ride back up. The station above, the Spéléo Gare, was built to the architect E. Pinetre's design in 1972 and renovated in 2022, and houses an exhibition hall and the shop.
How big is the chamber, and how deep does the route go?
Aven Armand is a single chamber, and its dimensions are the first thing to fix in your head, because photographs flatten them. It runs 110 metres long, 60 metres wide, and 45 metres from floor to the top of the vault — roughly 200,000 cubic metres of enclosed space. That 110 metres is a length rather than a depth, which is where descriptions of the cave most often go wrong. The depths are separate figures and worth keeping straight: the funicular sets you down 60 metres below the surface, the viewing balcony over the forest sits at 70 metres, and the chamber floor lies about 100 metres down. The 45-metre vault matters more than the number suggests, because it is what produced the formations beneath it.
Two vertical shafts define the cave. The aven itself — the natural opening that gives the site its name — is a vertical chimney 75 metres deep and about three metres across; it is the one Louis Armand descended by rope ladder in September 1897, and the one Exploration visitors still descend today. A second shaft drops a further 87 metres from the chamber and is blind, leading nowhere. Beyond the funicular, the visitor route is a 450-metre walkway with roughly 50 metres of height change, covered in about an hour, and involving around 200 irregular steps down and close to a hundred back up, all illuminated and fitted with handrails.
What is the Virgin Forest?
The floor of the chamber carries what the site calls the Forêt Vierge — the Virgin Forest — more than 400 stalagmites standing in one continuous sweep, which the operator describes as unique in the world. Individual formations frequently reach 15 to 20 metres. Martel's verdict after the 1897 survey was blunt: « Aucune grotte connue au monde ne possède rien de semblable » — no known cave in the world has anything like it. What makes the effect work is that this is one uninterrupted view rather than a sequence of small chambers. You look down on the forest from the balcony at 70 metres before descending into it, so you get the whole thing at once and then walk through it.
Lighting is a large part of the experience and has been reworked repeatedly. The original scheme was designed by Fernand Jacopozzi, the engineer who lit the Eiffel Tower; it was overhauled in 1992, and again in 2014, when LEDs and a sound-and-light presentation were installed. The current scheme wakes the chamber progressively as the tour moves through it, so the forest colours up in stages rather than being revealed all at once. Photography is allowed but flash is not, which means everything you shoot depends on that installed lighting. One thing you will not see: there are no bats. The natural openings are too narrow and too deep for them, and the funicular tunnel is gated.
What is the Grande Stalagmite?
At the centre of the forest stands the Grande Stalagmite, around 30 metres tall, which the operator describes as « la plus grande stalagmite connue du monde souterrain aménagé » — the tallest known in the developed, publicly visitable underground world. That qualifier is doing real work and deserves respecting: taller stalagmites exist in caves that are not open to visitors. Its estimated age is 300,000 to 400,000 years, and its size is attributed to the sheer volume of water that has fed it across that span. It is broad at the base and tapers along its length, rising towards the vault as a needle rather than holding an even cone all the way up.
It is also still growing, and it has somewhere to go. A stalactite hangs from the vault directly above it, and the operator estimates a further 200,000 years before the two meet and fuse into a single column roughly 50 metres tall. The rate involved is not guesswork. Martel measured the formations between 1897 and 1926 and recorded growth of one to two millimetres across those twenty-nine years — a primary measurement taken by the man who surveyed the cave, and the most concrete illustration on site of what deep time actually means. Stalagmite growth in the chamber is thought to have begun around 700,000 years ago, in a cavity that had already been underground for some 30 million.
Why do the formations look different from other caves?
Because of the 45-metre vault above them, and this is the single most useful thing to know before the descent. Water infiltrating from the surface arrives already saturated with calcite, picked up in contact with the topsoil of the Causse Méjean, and deposits some of its crystals at the ceiling before the drop even falls. What is left then falls roughly 40 metres and shatters on impact, spreading its calcite outward rather than trickling gently down — so the deposit builds in successive stacked reliefs, the characteristic plate-on-plate profile you see throughout the chamber. In caves where the fall is short, water simply runs down the formation and the surfaces stay smooth.
Colour is readable too, once someone gives you the code. White is pure calcite, and the whiter a formation is the more actively it is being fed by dripping water — so brightness is a live signal about the present rather than a matter of age. Ochre and brown come from humic acids carried down from the topsoil above. Grey comes from manganese. Together with the stacked-plate relief, that gives you a way of reading the forest rather than merely looking at it: which formations are still growing, which have been cut off from their water supply, and something about what the ground overhead is made of. The same water leaves calcite at the ceiling before it ever falls, which is why stalactites hang above the forest as well as growing beneath it.
What else is there to see, and which visit shows you most?
Not everything worth seeing is underground. The Spéléo Gare — the funicular station, built to E. Pinetre's design in 1972 and renovated in 2022 — houses an exhibition hall and the shop, which carries regional products. The Spéléo Café sources from local producers, and there are covered and open-air picnic areas; parking is free and takes all vehicle types. Allow about an hour for the Jules Verne visit itself and rather longer for the site as a whole, because the exhibition hall is the part most people underestimate. Close to ten million visitors have come through since the cave opened in 1927 — a cumulative figure across nearly a century, not an annual one.
Three alternatives change what you see. The Particulière is the same hour-long route with a private guide and the funicular privatised in both directions, advised for four to nine people and capped at fifteen. The Exploration visit, age twelve and over, takes you down the 75-metre natural shaft on ropes with professional instructors, headlamps and equipment provided — capped at sixteen people by the shaft and eight by the tunnel — and returns by funicular, running around two hours with a drink at the Spéléo Café and an exploration certificate at the end. A VIP visit privatises the whole cave, with lighting triggered step by step as you move. All three are arranged in advance rather than on the day.
Frequently asked
What is the main highlight at Aven Armand?
The Grande Stalagmite at the centre of the Virgin Forest — around 30 metres tall, estimated at 300,000 to 400,000 years old, and described by the operator as the tallest known stalagmite in the developed, publicly visitable underground world.
How big is the chamber?
110 metres long, 60 wide and 45 metres from the floor to the top of the vault — roughly 200,000 cubic metres. The 110 metres is a length, not a depth; the chamber floor lies about 100 metres below the surface.
How many stalagmites are there?
More than 400, collectively the Forêt Vierge or Virgin Forest, standing in one continuous sweep across the chamber floor. Individual formations frequently reach 15 to 20 metres, and the largest is around 30.
How deep does the funicular go?
Sixty metres, in one minute thirty, through a 208-metre tunnel. It is only the first stage: the viewing balcony is at 70 metres and the chamber floor about 100. It is compulsory in both directions on the standard visit.
Why do the stalagmites look stacked rather than smooth?
Because of the fall height. Water deposits some calcite at the ceiling, then the drop falls roughly 40 metres and shatters on impact, spreading calcite outward in successive reliefs. In caves with short falls, water trickles down and surfaces stay smooth.
How fast do the formations grow?
Very slowly. Martel measured growth of one to two millimetres between 1897 and 1926 — twenty-nine years. A stalactite above the Grande Stalagmite is estimated to need another 200,000 years to meet it and form a 50-metre column.
Are there bats in the cave?
No. The operator states there are none: the natural openings are too narrow and too deep, and the funicular tunnel is gated. The doors at both tunnel ends also hold the microclimate steady at about 12°C and 90% humidity.