Cave of the Crystals or Giant Crystal Cave is a cave connected to the Naica Mine 300 metres (980 ft) below the surface in Naica, Chihuahua, Mexico.

One of the world's most spectacular geographical discoveries was the cave of giant crystals with its selenite crystals of a size never seen before. most of them measure six meters in length, with some of them reaching eleven meters. the temperature at this depth varies from 45°C to 50°C, while the percentage of humidity ranges from 90 to 100%, meaning that human beings cannot survive there for longer than two hours.