National Geographic Adventure named the diving at Bonne Terre Mine in Missouri one of the top 10 adventures in America, and it’s easy to see why. Back in the day, the mine’s deepest reaches were not underwater. A massive pump system stemmed the flow of encroaching groundwater as the miners pushed ever deeper. But when this, the world’s largest lead mine, was all mined out, the pumps were turned off and water trickled in to fill the void. These days, mine owners Doug and Catherine Goergens maintain a constant water level, providing divers with access to their unique underwater vision.