Exploring One of the World's Largest Caverns by Drone

ABC's Ginger Zee went inside a hidden world located in a mountain inside a jungle in central Vietnam.
2:28 | 05/14/15

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Transcript for Exploring One of the World's Largest Caverns by Drone
Tonight our ginger zee takes us to one of the most magnificent buried treasures deep inside a mountain inside a jungle on the other side of the planet. Getting there is a gigantic undertaking. But as you're about to see with a little help from some spectacular drone footage, it is so worth the effort. Reporter: We entered through claustrophobic crevice. Then it opens up and drops down and down. At the bottom I feel like I've landed on another planet. A subterranean rushing river. Now I find myself in mother nature's sculpture garden, filled with prehistoric Boulders and stalagmites, gigantic columns built up by calcium-dripping water. You can see me about 400 feet below the top of one of the world's largest caverns. Inside a mountain in central Vietnam and was only found a couple of decades ago. After a grueling hour, an illuminating light 1,000 feet overhead. Every turn there's something else. This colossal sky light where the chamber ceiling collapsed is called a dolight. It's a lush, green oasis. Sand beaches lit up below. It looks like "Avatar" in here. It doesn't feel real. No. This is that hidden world we've been chasing. Sondong or mountain river caves, the planet's largest. Just look at this! It is unbelievable! I'm standing on a colossal stalagmite, the jewel in the crown of sondong cave. We press on. Suddenly I'm in a jungle under a second monster sky light. Not atop a mountain but inside it. You don't normally get trees and jungles in caves. That's why it's quite different. Jungle plants and animals from above adapting to this unique subterranean netherworld. What a view from those drone cameras. Breath-taking beauty like a fantasy world come to life. The punishing journey worth every ounce of sweat. It's something this grandiose was just found, imagine what's is out there. Gorgeous. Our thanks to ginger zee for that stung report and to you for

This transcript has been automatically generated and may not be 100% accurate.

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