1000 feet under ground, NGC goes inside one of the greatest natural marvels on the planet - a giant crystal cave described as Superman's fortress, with magnificent crystals up to 36 feet long and weighing 55 tons. A team of experts ventures into the cavern, enduring scorching-hot temperatures that could kill a human after just 15 minutes of exposure. They'll push the boundaries of physical limitation to explore a crevasse that could lead to another - and perhaps more spectacular - crystal cave. The Crystal Cave is located in a tiny Mexican mining town called Naica, 250 kilometers (150 miles) south of the US border, in the heart of Chihuahua.

Film Duration: 01:31