Fosse Dionne – Tonnerre, France - Atlas Obscura

Fosse Dionne

Tonnerre, France

This natural French spring has been turned into a magical grotto by Roman and medieval constructions. 


Nestled in the quaint Tonnerre district of France, the ancient wellspring known as the Fosse Dionne is a deep natural water source that has been built up into a haunting grotto since Roman times. 

Located near to a small hotel that bears its name, the “Dionne Pit” is a lovely historic spot. The gurgling sinkhole was used in Roman times to supply clean water to a nearby palace, and became the focal point around which much of the ancient settlement developed. During the 18th century, a stone rim was built around the pool, with a spout at one end to allow the water to run off. A squat amphitheater was built behind the pool, and it was used as a public laundry. These constructions remain to this day, a bit of crumbling masonry and moss, adding to the spring’s natural beauty.    

The waters that pour from the natural font are thought to originate from somewhere in the Morvan mountains, but due to the tight passages that taper off the deeper the pit gets, divers have never been able to reach the actual source. For a time, modern divers were allowed to plumb the depths of the hole in search of artifacts and geological information, but after a series of fatalities in the depths of the pit, diving access is only allowed with permission of the Mayor of Tonnerre.

The spring gently produces water during the summer months, and tends to get more vigorous during spring as snow melt comes cascade out through the whole. However, no matter when one visits the pool is equally tranquil and evocative.

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