SONEPUR, INDIA - NOVEMBER 15: An elephant is painted in decorative colours during the Sonepur Mela on November 15, 2011 in Sonepur near Patna, India. The cattle fair, held in the Indian state of Bihar, has its origins during ancient times, when people traded elephants and horses across the auspicious river Ganges. The mela used to attract traders from places as distant as Central Asia. It is one of Asia's largest cattle fairs and lasts for a fortnight. (Photo by Daniel Berehulak/Getty Images)

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.