At one time the Bonne Terre Mines were the world's largest producer of lead ore, but after suddenly striking water and completely flooding the underground chambers, the site is now the world's largest freshwater dive location.
Digging at the Missouri mine began in 1870 to access the rich deposits of lead. Huge underground chambers were created as workers collected the ore, and huge pieces of mining equipment were installed along with railway lines to shuttle the rock aboveground. The caves and tunnels quickly became the largest man-made underground chamber in the world. Despite the massive Dwarven creations, operations quickly came to a halt in 1962 when underground water was struck and flooded miles of the caverns, drowning millions of dollars of equipment and rendering the mine unusable.
Now the mine has been reopened as one of the most unique diving areas in the world. Due to the toxic lead particles in the water, nothing can grow rendering the liquid astonishingly clear. Piercing lights have been installed throughout the caverns illuminating over 100 feet into the waters. Across 24 different diving paths covering 17 miles of subterranean rooms, visitors can swim through the grand arches and towering drowned chambers and check out the rusting equipment still at the bottom of the "Billion Gallon Lake."
There are also walking and boat tours in the portions of the mines that can support them so the underground grandeur isn't just for professional divers. The Bonne Terre Mines may have begun as a wonder of industry but now the mine is closer to the wonders of Atlantis.