The Grottes de Neptune hide a yet to be explored lake

The Grottes de Neptune hide a yet to be explored lake

Grottes de Neptune, Couvin

An underground lake is hidden in the Grottes de Neptune and remains unexplored today, despite attempts by cavers.

“‘The water takes 48 hours to flow out of the cave. That’s nearly 2 km, that’s excessive, there is definitely an underground lake there”, says Pascale Somville, caver. And yet, it has been several years since the area of the Grottes de Neptune has been explored.

Pascale Somville is one of around 15 cavers active in the Groupe Spéléologique de Charleroi [Charleroi Caving Club], one of Belgium’s oldest caving clubs. They meet at Petigny once or twice a year to explore the Grottes de Neptune.

“After the lake which tourists cross on a boat, there is a passage to the siphon. There, we can see cracks. We tried to slip through but it’s too narrow for a human”, continues Pascale Somville. “There are small passages or areas filled with water, it’s impossible for cavers to go any further”.

The grottes de Neptune can be experienced by way of sound and light shows

The last known point in the caves for accessing the lake

“Divers have explored the siphon”, continues Pascale Somville. “They have been to a depth of around 10 metres and then it was impossible to go any further”. She is thoughtful : “But one day, we’ll find it…

Whilst waiting to access the lake, the research continues. Studies by the Universities of Mons and Namur have shown with fluorescein colouring that the water flowed for more than 2.5 km underground before emerging on the surface.

We tried different passages, but all to no avail

The cavers explore the Grottes de Neptune once or twice a year

Thousands of underground discoveries yet to be made

To try and find this famous lake, the latest explorers tried several techniques. Firstly, entering via the secondary tunnels, but these were too narrow for a human.

Then, breaking various layers with a crowbar or by hand, except that the rock is much too hard. “You would have to break it with explosives. We don’t have the skills”, ’ she says. A Flemish club tried to get in with dynamite, but they quickly gave up due to the hardness of the rock. “Sometimes, all you need is luck…”

Tours of the Grottes de Neptune end with a boat trip

Enjoy being underground

Whilst waiting for this lake to be discovered, the caves can be explored thoroughly. They are around 2 km long, with two tunnels, the smaller one is 422 metres long and the larger one is 1,080 metres long, with the addition of a few chambers. The large chamber is more than 19 metres high, from floor to ceiling. “The pleasure from caving does not necessarily come from crawling or slithering through tiny passages – in fact, I avoid it, I am a touch claustrophobic – , but rather from discovering large secret underground chambers”, says Pascale Somville.

We feel a bit like the last explorers of the world discovering the depths of the earth

Another pleasure for cavers: observing the fauna and the flora. Here, in the caves, we can see stalagmites and stalactites but also bats, insects, spiders, butterflies, niphargus (a sort of small prawn which is not eaten). “We count up to 6 – 7 species of bats, or around 30 chiropterans. With those hidden, we estimate that there are 4 times as many,”, explains Daniel Lefebvre, another caver.

And for those who don’t have any caving equipment, it is entirely possible to visit the Grottes de Neptune, on foot and by boat.


Grottes de neptune
Rue de l’Adujoir, 24
5660 Couvin
+32 (0)60 31 19 54

©Pictures/Christophe Vandercam