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 venture 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.