Cave of Crystals, Naica, Mexico
The Cueva de los Cristales, 300m under the ground in the remote area of Naica, Chihuahua, contains extraordinary giant selenite crystals, some of the largest ever found in the world. The longest so far measures 12m, 4m in diameter and weighs 55 tonnes. The cave was discovered by accident in 2000 by miners drilling for silver and lead. Temperatures in the cave reach 58C with 99 per cent humidity, so it remains relatively unexplored – but it’s a source of fascination for scientists and geologists trying to unlock its secrets.