SHAMBHALA IS THE OLDEST and purest vision of enlightenment, a prophecy that became a place and, finally, a legend. Varieties of the myth are shared among Indian Hindus, Chinese Taoists, and Tibetans of both Buddhist and Bon persuasions. It is the Ultima Thule of the East, a promise that a golden age will be restored by the king of a great northern paradise, riding forth on a white horse to destroy the barbarians of the world, to stamp out materialism and immorality and bring an end to this dark cycle of time. It is, in other words, what human beings need to believe in. A promise of eternity, and the return of hope.

From one of its earliest mentions, written perhaps before 300 B.C. in the Mahabharata, the first Hindu epic, the legend of Shambhala took more than a thousand years to reach neighboring Tibet. There it found its greatest guardians as the Tibetan Buddhists transplanted the myth into Nepal, Sikkim, Mongolia, Ladakh, and as far afield as Beijing. The Tibetans claimed that the Kalachakra, the secretive mixture of tantric scriptures and meditation doctrines that form the highest teachings of Tibetan Buddhism, was sent to them by the King of Shambhala, using the ninth-century equivalent of express mail. They filled their holy books with descriptions and dashed off instructions for reaching the lost land.

Shambhala is a moving target. The Hindus thought it was up toward Nepal, the Nepalis in Tibet, the Tibetans in the northern deserts, always somewhere farther than the known. Yet seeking to actually find Shambhala here, on this earth, is really not unreasonable. Unlike the Christian heaven, Shambhala is an earthly paradise, solidly grounded on the surface of this planet. The current Dalai Lama insists the kingdom is real: "If so many Kalachakra teachings are supposed to have come from Shambhala," he has said, "how could the country be just a fantasy?" Contemporary Tibetan monks have posited that Shambhala can be found in Siberia, or at the North Pole.

I had a little help—from scholar Edwin Bernbaum, director of the Sacred Mountains program at the international nonprofit Mountain Institute and author of the definitive book on the subject, The Way to Shambhala. When I called Bernbaum at home in Berkeley, California, to ask where Shambhala could be, he first played hard to get ("Right here," he said, laughing; "if you could really be present, Shambhala would be right here.") and then put his figurative thumb on a map of western China.

Whatever lost city or ancient kingdom had inspired the Tibetans to pin the wandering myth of Shambhala onto one particular plot of earth, it was probably there, he said. The Tibetans' Kalachakra teachings had come from Central Asia in the late first millennium, almost certainly composed in monasteries along the Silk Road. Decoding the scriptures and cross-checking them with archaeological evidence, Bernbaum had found a "likely historical prototype," one "interesting kingdom" that had thrived as a center of Buddhist scholarship, only to disappear under a wave of history just as the Tibetans were grappling with its teachings. City and paradise were conflated.

Bernbaum had been there himself, he said, in the 1980s, although travel restrictions had kept him from making the original pilgrimage north, from Tibet itself. I was in a better position. With borders open, I could attempt the ancient route spelled out in Tibetan texts.

Several guides to Shambhala were written over the centuries. There was a thousand-year-old passage in the Tengyur, part of the Tibetan canon of holy books; an account by a 13th-century lama named Manlungpa ending in the almost casual mention that he'd been there himself; and a florid 1770s description by Palden Yeshe, the third of the Panchen Lamas, said to be pre-incarnations of Shambhala's future king. But the most affecting was a desperate plea for help, a letter called "The Knowledge-Bearing Messenger," written around 1560 by a Tibetan prince named Rinpungpa.

One cold winter day, I drew out a rare copy of the prince's letter from the closed stacks of the New York Public Library. The manuscript, written in medieval Tibetan, was printed on long, loose-leaf pages that mimicked the palm leaves used in ancient Buddhist books. I had brought a red-robed monk, a young Tibetan from Staten Island, to attempt a translation, and when I unwrapped the book in his presence, a crowd of hushed bibliophiles gathered to watch.

Rinpungpa was surrounded by enemies, his world collapsing. Buddhism was no longer practiced in India, its land of birth, and Islam had conquered Afghanistan to the west and the Central Asian steppe to the north. Rinpungpa's own clan had ruled brutally, and the prince correctly surmised that his days were limited. Seeking help, he summoned a spirit messenger to reach the enlightened kingdom, where his own father would be waiting, reborn in paradise.

Take this message and go to my father in Shambhala. May my words of truth, conquering the mountains of dualism, guide you along the way and help you to overcome the obstacles that lie before you.

Rinpungpa filled long passages with colorful accounts of the route across Tibet and Central Asia, warning of everything from starvation to forests made of knives to rivers so cold they killed you at first touch. Adding in the Tengyur and the other ancient texts, the directions pretty much boiled down to this: Go from the lowland Indian river valleys where the Lord Buddha lived, up to Kathmandu's ancient kingdoms, and climb onto the roof of the world, crossing Tibet westward, via its greatest monasteries and the sacred mountain of Kailas. Then head north, over an "outer ring" of sky-high ice mountains, across a vicious desert, past jade city-states, into unknown vistas. All the while you must appease dozens of gods, accumulate merit and fend off monsters, suppress the demons of delusion and transcend mere xistence, recite 99 million mantras and fly through the sky on a fire chariot, only to reach an "inner ring" of snowy mountains so high that even an eagle cannot cross. Beyond there, you must choose rightly among high valleys and low cities, having the good sense to know Shambhala when you reach it.

Using the ancient texts, and Google Earth, I calculated this at 3,400 miles. Rinpungpa's letter would lead me through three countries, a dozen languages, and many peoples, past the world's highest mountains and down into the bottom of the lowest desert in Asia.

Six weeks, I told my wife. All the way to heaven, and then home.

Perhaps I would not make it; perhaps I would fail in some, or every, way. But one must go oneself to know the truth.