Deadly Crystal Cave

1000 feet below Naica, Mexico is a lead, zinc, and silver mine in which scientists have found a cavern filled with some of the largest gypsum crystals anyone has ever seen. Uncomfortably, however, the cave is also filled with air up to 136 F and humidity above ninety percent making exploration more than a little hazardous. Luckily, the National Geographic explorers documented the cave before it was supposedly refilled to allow the crystals to remain undamaged and possibly continue growing even larger.