Nearly 1,000ft below the Chihuahua Desert in Mexico, there is a cave of Crystals. It is discovered by two brothers drilling in the Naica lead and silver mine. Up to 170 giant, luminous obelisks - the biggest is 37.4ft long and the equivalent height of six men. The giant obelisks are formed from groundwater saturated in calcium sulphate which filtered through the cave system millions of years ago. Because the crystals resemble giant icicles, the picture suggests it must be very cold inside the Cave of Crystals - but appearances can be deceptive. In fact, the temperature is a sweltering 112F, with a humidity of 90-100 per cent. The picutures looks amazing!!