For centuries, the mysterious Lake Pavin has been the stuff of legend, due to its seemingly unfathomable depth. An infernal abyss for some, the site of a city swallowed up by divine wrath for others, it was described in the 17th and 18th centuries as a bottomless lake, devoid of fish and deserted by men. It was said that throwing a stone in the middle of its waters would trigger lightning, thunder, and even a huge geyser.