Vietnam's Son Doong cave is big enough for a skyscraper to fit inside | 60 Minut [10:05-12:57]

McNabb couldn't back out. A partner found him and used a knife to rip away his coat to give him the spare half-inch. He needed. Did he pull you out by your feet? Pretty much. Yeah. You are still exploring this region? Yes, yes. We've come back every two years and we've barely scratched the surface of the caves in this area. There may be another biggest cave in the world. That could well be. Truth is, McNabb's first expedition in 2009 never reached the end of Sondong. Beyond this underground lake, he discovered a 30-story wall and ran out of time before he could scale it. Taken, taken, taken. We climbed it on our track and understood immediately why they call it the Great Wall of Vietnam. Keep the line tight, taken, excellent, taken on the like line. It's a 300-foot climb on slick rock with no foothold anywhere. Taken, excellent. It's got that really good from right up to the corner. It's challenging enough until you realize, of course, you're doing it in the dark and it's essentially raining. The groundwater is coming from the roof. So with everything wet, you find yourself slipping back while climbing up. And our team got us up and over, drenched and a little exhausted. Well, we saved the best for last. We've made it all the way through nearly all the miles of the cave over three days. And now we just have a little bit further to go. In fact, I can see the exit from here. We could see it that white up there, but we still had quite a climb to make. We learned by the end of our trek that Sundong may be even larger than we know. Hundreds of feet below that lake behind us, the water is draining somewhere. There could be more caverns beyond. It's the work of millions of years likely to continue for millions more. Unimaginable time. Unshared by a pendulum of light, illuminating the splendor of one of the greatest marvels on or under the earth.