In the heart of France’s idyllic Burgundy region, surrounded by manicured vineyards, fortified Renaissance chateaux and medieval hill towns, sits one of the bucolic area’s most mysterious attractions: a seemingly bottomless spring-fed pit in the small town of Tonnarre known as the Fosse Dionne. A torrential 311 litres of water gush from this gaping well every second, but despite countless explorers venturing into its depths over the centuries, no-one has ever been able to find its true origin.
The Romans harnessed the karst spring for drinking water; the Celts considered it sacred; and the French enclosed its ever-changing turquoise, blue and brown pool in a circular stone rim with an amphitheatre and used it as a public wash house in the 1700s. It was at this time that the women who peered down into Fosse Dionne’s depths while washing began to wonder what lurked at the bottom. According to one legend, a deadly serpent patrolled the well’s base. According to others, the spring was a portal to new worlds.
In an effort to solve this age-old mystery, two professional divers descended into the limestone rocks’ tight passages in hopes of reaching its source in 1974. While navigating the spring’s twisting, tapering chasms, they perished. In 1996, the town hired another diver to attempt the descent. He also died.
Then, last October, after deeming the spring too dangerous to dive for years, Tonnarre’s mayor hired professional diver Pierre-Éric Deseigne. Remarkably, he descended more than 70m underground, venturing 370 total metres from the cavity’s entrance – all while filming his expedition. While Deseigne explored territory that no-one had ever seen before, he still was unable to locate the spring’s source, leaving France’s ancient underground mystery unsolved.
This video is part of BBC Reel’s Hidden Histories playlist.
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