Cueva de los Cristales (Cave of the Crystals) is a cave of the Naica Mine in Chihuahua, Mexico. The chamber contains giant selenite crystals, some of the largest natural crystals ever found. The cave's largest crystal is 11 m (36 ft) in length, 4 m (13 ft) in diameter and 55 tons in weight. The cave is about 30 m (98 ft) in length, 10 m (33 ft) in width and almost 300 meters (900 feet) below the surface of the Earth. It is extremely hot in the cave with air temperatures reaching up to 43 °C (109 °F) with 90 to 100 percent humidity. The hot temperature is due to the proximity of a magma chamber.The cave is relatively unexplored because humans can only survive for approximately ten minutes without proper protection and only 45 with special equipment. Add to that the risk of falling into deep pits, ending impaled on a sharp crystal.