Journey to one of Earths few landforms visible from space, a World Heritage site, and one of Americas most popular National Park with over nearly five million visitors a year. For scientists it is a place of baffling mysteries. How and when was it actually formed? Why does one of the planets deadliest diseases still endure in the Canyons premier carnivore the majestic mountain lion? What drove one of the largest birds on earth, the California Condor, to the brink of extinction? National Geographic joins a rare scientific odyssey down the Grand Canyons entire 277-mile length through some of the most treacherous rapids on the planet to try to unlock the mysteries of this great unknown. From the river still cutting through two-billion-year-old stone to the creatures roaming its incomparable back-country, the Grand Canyon still has secrets to tell.