5) Naica Mine

·         Naica Mine (Cave of Crystals) – Mexico:

The Naica Mine of the Mexican state of Chihuahua is a working mine that is best known for its extraordinary selenite crystals. The Crystal Cave of Giants was accidentally discovered in 2000 by miners working in the silver and lead mine at Naica, Mexico. It lies almost 300 m (900 ft) below the surface of the Earth and it contains the largest crystals known in the world, by far. The largest crystals are over 11 m long (36 ft) and weigh 55 tons. It is still incredibly hot in the cave due its proximity to a magma chamber, deep underground. The air temperature is 50C with a relative humidity of over 90%, making the air feel like an unbearable 105C (228F) Entering the cave without special protective suits can be fatal in 15 minutes.