Cave of the Crystals or Giant Crystal Cave is a cave connected to the Naica Mine 300 metres (980 ft) below the surface in Naica, Chihuahua, Mexico. The main chamber contains giant selenite crystals (gypsum, CaSO4·2 H2O), some of the largest natural crystals ever found. The cave's largest crystal found to date is 12 m (39 ft) in length, 4 m (13 ft) in diameter and 55 tons in weight. The cave is extremely hot with air temperatures reaching up to 58 °C (136 °F) with 90 to 99 percent humidity. The cave is relatively unexplored due to these factors. Without proper protection people can only endure approximately ten minutes of exposure at a time.

MELBOURNE, AUSTRALIA - DECEMBER 26: A sand sculpture entitled 'Beetlemania' carved by Brad Goll from the USA and Karen Fralich from Canada is seen at the Creepy Crawlies Sandsculpting Exhibition on the Frankston waterfront on December 26, 2010 in Melbourne, Australia. International sand sculpture artists from around the world teamed up with their Australian counterparts to create the insect themed exhibition that will be open to the public until April, 2011. (Photo by Graham Denholm/Getty Images)