By Cailey Rizzo
September 14, 2017

Seventeen years ago, two brothers who worked for Industrias Peñoles were mining a tunnel underneath the Naica Mountain in Chihuahua, Mexico. They accidentally stumbled upon the Sistine Chapel of Crystals.

Naica’s Cave of the Crystals is an unlikely, magical discovery, buried 300 meters below the earth’s surface. Inside, gigantic crystals can reach science-fiction lengths of over 36 feet. Some of the heaviest crystals are estimated to weigh up to 55 tons.

Credit: Carsten Peter/Speleoresearch & Films/National Geographic/Getty Images

Researchers believe that the largest crystal inside the cave has been growing for over 500,000 years.

The crystals have been growing to epic proportions thanks to a prime combination of conditions over the past 10,000 years. Inside the cave, temperatures can reach up to 136°F, with 90 to 99 percent humidity. The air is acidic and there is no natural light. Groundwater laced with calcium sulfate swam into the caves and, heated from magma below, began to form the gigantic assembly of crystals.

Credit: Carsten Peter/Speleoresearch & Films/National Geographic/Getty Images

However, the conditions, while great for crystals, are perilous for people. Anyone who enters the cave must wear a special cooling suit and limit their time spent in the cave to only 45 minutes.

Credit: Carsten Peter/Speleoresearch & Films/National Geographic/Getty Images

The caves are currently closed to tourists, as mining operations stopped and the underground cavern re-flooded with water. Conditions are returning to their undisturbed state, allowing the crystals to continue to grow.

Although the caves are closed, it is possible to see one of the crystals up close. In New York City, the Astro Gallery has a 32-inch Selenite crystal from the Naica on display.

Credit: Courtesy of Astro Gallery

And it’s not out of the questions that the caves will reopen, seeing as some very special visitors with government or scientific connections have been known to gain access.