Trou du Diable

Trou du Diable ("Devil's Hole") is a small sea cave carved into the cliffs of the Corniche Vendéenne, on the Atlantic coast between Saint-Hilaire-de-Riez and Saint-Gilles-Croix-de-Vie, near Sion-sur-l'Océan. It has been a protected natural site since 1926 and remains one of the best-known landmarks along this stretch of the Vendée shoreline.

How did the cave form?

The cliff here is made of Silurian schist, a crystalline rock that offers little resistance to wave action. Over time, the sea hollowed out a chamber inside the rock, topped by a narrow opening in the roof through which spray and water shoot upward when the swell is strong. That hole in the stone ceiling is what gives the site its name.

Why is it called the "devil's cauldron"?

Locally, the cave is also known as the "marmite du diable" — the devil's cauldron. As the tide rises, seawater surges into the chamber and churns violently, bubbling as if boiling in a pot, before being forced up and out through the opening above like a geyser. The display is at its most dramatic a few hours after low tide, when waves enter the cave at the right angle and pressure builds inside.

The legend behind the name

The site is tied to one of Vendée's oldest folk tales, the legend of the bridge to Île d'Yeu. According to the story, the devil offered Saint Martin a bargain: he would build a bridge linking the mainland to the island overnight, in exchange for the soul of the first creature to cross it — provided the work finished before the rooster crowed. The devil recruited fairies and imps to help, and even tried getting the rooster drunk so it would stay silent. The bird crowed through the night anyway, throwing off the construction schedule. At dawn, Saint Martin released a black cat onto the unfinished bridge, chased by a dog, and the cat became the first to cross. Furious at losing the wager, the devil kicked the cliff at this exact spot, tearing open the hole that bears his name. A second version of the tale holds that the devil was instead trapped inside the cave, guarded by five monks who were turned to stone — the rocks known today as the "five pineaux," which still rise from the sea off Sion-sur-l'Océan.

Is it safe to visit up close?

The setting is striking but the site carries real risk: slippery rock and unpredictable waves have caused accidents in the past. The town of Saint-Hilaire-de-Riez has installed guardrails along the clifftop. Until 2010, visitors could walk out onto a rock arch spanning the opening, but that crossing has since been closed off and barriered for safety.

How do you get there?

Trou du Diable sits along the Corniche Vendéenne footpath, a popular coastal walking route running along the cliffs between Saint-Gilles-Croix-de-Vie and Saint-Hilaire-de-Riez. The walk to the site and back takes only a matter of minutes from either town, passing other rock formations along the same stretch of coast, including the five pineaux mentioned in the legend.

FAQ

What is Trou du Diable? A natural sea cave in the cliffs of the Corniche Vendéenne, in the municipality of Saint-Hilaire-de-Riez, known for the opening in its roof through which water is forced up at high tide.

Where does the name come from? From a Vendée legend in which the devil, having lost a bet with Saint Martin over building a bridge to Île d'Yeu, kicked the cliff in anger and tore open the hole.

Can you go inside the cave? No, the rock crossing over the opening has been closed since 2010 for safety reasons; the site can only be viewed from the protected clifftop path.

When is the best time to see it? The "boiling cauldron" effect is most visible at high tide and during a stronger swell, a few hours after low water.

How do you reach the site? On foot along the Corniche Vendéenne path, which connects Saint-Hilaire-de-Riez and Saint-Gilles-Croix-de-Vie near Sion-sur-l'Océan.