WATCH: 66 Life-Changing Hours of Agoge in Mongolia

Based on the arduous training of children in ancient Sparta, in which they were groomed to become warriors for future army service, the Spartan Agoge is the ultimate test of mind, body, and spirit. It is, quite simply, the pinnacle of endurance challenges.

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There have been modern-day Spartan Agoges in some of the most fascinating, exotic, culturally significant locations on Earth, from under the northern lights in Iceland to the picturesque mountains of Japan to the Great Wall of China. In 2018, the Agoge came to Mongolia, a breathtaking country that has produced some of the most notorious conquerors and fiercest warriors the world has ever known. It was a natural, perfect fit.

"There’s not a lot of places left on Earth where you can have a true adventure," Spartan Vice President of Product David Watson says. "Mongolia is the perfect mix of historical and cultural elements that blend with Spartan’s values."

Over the course of 66 grueling hours, 40 Agoge students from all walks of life and all corners of the Earth put themselves to the test. Led by taskmasters, called Krypteia, they traversed the landlocked East Asian nation, from Ulaanbaatar (the country's capital) to Khentii Province (Genghis Khan's birthplace). They took on six grueling missions, including a Bökh wrestling competition, a 380-meter swim in brutally cold water, and shooting flaming arrows.

More: The Spartan Kids Death Race Itinerary: 24 Hours That Will Change Your Child's Life

“It’s about changing your life, and that’s what happened," Bryan, a graduate, says of the life-altering experience. "I didn’t give up. I didn’t stop and I didn’t quit. I complained. I shivered. I took all of my clothes off to help somebody that was in true need. And it’s just ... It's a very overwhelming experience."

Watch the full documentary, chronicling the entire 66-hour expedition, above.