In the summer of 1889, young caver Édouard-Alfred Martel descend into this well, 338 feet (103m) deep, whose infinite blackness seemed to open into hell itself. The adventurer, emboldened by the tales of novelist Jules Verne, found a labyrinth of galleries, with a river system running through them of dark water that brightened to a cobalt blue in the flickering light of his candle. Further in, he came upon chambers with cathedral-like vaults, gleaming with iridescent stalactites. Today, brave visitors, descending on foot or by elevator, can discover this majestic site for themselves.