Vietnam's Son Doong cave is big enough for a skyscraper to fit inside | 60 Minut [0:00-5:01]

Imagine in the 21st century discovering a marvel on par with Mount Everest or the Grand Canyon. It happened in 2009 with the revelation of the largest cave passage in the world. It's in Vietnam, and they call it Hang Song Dong, Mountain River Cave. An intrepid British explorer, Peter McNabb, led the first team through this epic underworld of caverns, the height of skyscrapers. McNabb is to caving what Armstrong is to the moon, the first explorer. Recently, we asked McNabb to show us this wonder of the world. But before we begin our trek, we really have to show you a preview of where we're going. Simply glorious. This was the moment Song Dong caught us in its grasp. Sunbeams cascading 120 stories from a break in the ceiling, groundwater above us slipping through the light like rain, and rock reflecting what seemed like the only sound in the world. Not many have stood in this space that transcends time. It was a reward for our journey that began days before. The only way to Song Dong is on foot, a trek of a day and a half. He had a party of 53 moving in groups, mostly porters heaving, camping and TV gear, plus experts in safety and climbing. There were 20 river crossings, water flowing through limestone, two of the essentials for building caves. This is the slender center of Vietnam, the Chusun range between Laos and the South China Sea. We were following the Vietnam War's Ho Chi Minh Trail, through a jungle where tigers are not unknown, and leeches are plentiful. Finding us were explorers howard Limbert, whose work in Vietnam over 30 years discovered 500 caves, and Peter McNabb, whom Limbert sent to be the first in Song Dong. I find it an adventure going exploring, and not quite knowing what's around the corner and just sort of finding your way through, and things reveal themselves like big chambers, or passages, or tight narrow bits, beautiful formations. And there aren't a lot of places on earth that you can discover for the very first time. No, you have to look pretty hard for them. You have to look pretty hard for the entrance to Song Dong. You'd hardly notice, but for the writing on the wall, proclaiming the miracle of Ho Con. In 1990, Ho Con, a villager, discovered this entrance after he sheltered here from a storm. He told us, I was collecting wood, I saw a sinkhole, and I felt something strange. The strange feeling was wind blowing out of the ground. As no, that's the breath of a tremendous cavern. In 2000, the British cabers asked young Ho Con to show them, but it took eight years he'd lost it in the trackless jungle. In 2008, I finally found it, he told us. In 2009, they started exploring. That exploration began here. They were just inside looking back toward the entrance above. The first obstacle is a spectacular 30-story wall that our climbing team showed us how to descend. Do you step to the left side? Darkness would be nearly total, but we lit it so you can see. Peter McNabb was the first to do this. In 2009, he and four others on his team were dropping into darkness. There's an obvious, big black hole where you're heading towards, and you just sort of skirt