BBC – Voyage – La Fosse Dionne: the mysterious underground source of France


In the heart of the idyllic region of Burgundy, surrounded by manicured vineyards, fortified Renaissance chateaux and medieval hill towns, lies one of the bucolic region’s most mysterious attractions: a seemingly bottomless pit fed by a spring in the small town of Tonnarre known as Fosse Dionne. A torrent of 311 liters of water gushes out of this yawning well every second, but despite the countless explorers who have ventured into its depths over the centuries, no one has ever been able to find its true origin.The Romans exploited the karstic spring to drink water; the Celts considered it sacred; and the French enclosed its ever-changing turquoise, blue and brown swimming pool in a circular stone rim with an amphitheater and used it as a public washhouse in the 1700s. It was at this point that the women who scanned the depths de Fosse Dionne, washing themselves, began to wonder what was hidden at the bottom. According to legend, a deadly snake patrolled the base of the well. According to others, spring was a portal to new worlds.

In an effort to solve this age-old mystery, two professional divers descended into the narrow passages of the limestone rocks in the hope of reaching its source in 1974. Navigating the twisting and tapering chasms of the source, they perished. In 1996, the city hired another diver to attempt the descent. He is also dead.

Then, last October, after having judged spring too dangerous to dive for years, the mayor of Tonnarre hired professional diver Pierre-Éric Deseigne. Remarkably, he descended more than 70 meters underground, venturing a total of 370 meters from the entrance to the cavity – while filming his expedition. While Deseigne explored territory no one had seen before, he was still unable to locate the source of the spring, leaving France’s ancient underground mystery unsolved.

This video is part of the BBC Reel Hidden Stories playlist.

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