National Geographic went 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. Our presenter, Angie Lucht, was one of the four cavers/mountain rescuers on the team that went into the caves. She will talk about the boundaries of the physical limitations and new explorations while filming "Into the Lost Crystal Caves". You can see photos and video clips from the documentary here.