slate.com – Atlas Obscura on Slate is a blog about the world’s hidden wonders. Like us on Facebook and Tumblr, or follow us on Twitter.

In 2000, two miners drilling an excavation tunnel below Chihuahua, Mexico discovered something truly astonishing.

Within this cavern, exposed when the mining company pumped out groundwater, the miners found crystals measuring up to 12 meters (almost 40 feet) long and weighing up to 55 tons. They were 20 times bigger than the largest crystals anyone had seen before. It was one of the most spectacular mineralogical discoveries ever made. They named it the “Cueva de Los Cristales,” or the Cave of the Crystals.