Alexander Van Driessche, “The Naica Mine”, Mexico

In 2000, stunned geologists discovered some of the largest crystals ever found in the then-working Naica Silver Mine in Chihuahua, Mexico. Nearly 1,000 feet underground, selenite crystals as large as 4 feet in diameter and 50 feet long grow in an atmosphere of 136 degrees Fahrenheit and 90-99 percent humidity. Only a handful of people has ever entered one of the five crystal growing caves. In 2015, the mine ceased operation and was closed to the public after a worker suffocated in the inhospitable environment while trying to steal some of the selenite.