Giant Crystal Cave (Cueva de los Cristales) is a natural formation in the Mexican city of  Naika, Chihuahua. It is located at a depth of more than 300 meters under the ground. It is unique because huge transparent crystals of selenite intertwind (a crystalline variety of gypsum) and reach record sizes. Giant formations have existed for several hundred thousand years and grew in the underground water filled with water. Geologists call this Mexican miracle "Sistine Chapel of Crystals" because of its beauty and uniqueness.