After you read Baker's book, the reasons for that enduring mystery become obvious. The gorge -- located in the Pemako region of Tibet -- is forbidding in ways that would seem unsubtle in an Indiana Jones film. It's rife with snakes, tigers, leeches, landslides, raging rapids, insane weather, competing explorers, petty Chinese officials and cultists who believe they can steal your karma by poisoning you.

But, as in any good Indiana Jones film, hidden treasures lay beyond the pitfalls. In the 19th and 20th centuries, British explorers such as Frank Kingdon-Ward were obsessed by Pemako's uncataloged geography and plant life. And Buddhist legend tells of a sacred land, or beyul, hidden in the heart of Pemako -- complete with one or more magic waterfalls, rainbow-choked valleys and sacred plants that confer enlightenment if "auspicious circumstances" converge. (The beyul legend informs the Shangri-La of "Lost Horizon.")

"The Heart of the World" is Baker's memoir of his obsessive, decade-spanning quest to explore the gorge's spiritual and geographic enigmas. He's a mountaineer and a Buddhist scholar, which put a double prong on his mission -- he wanted to chart the five miles of the Tsangpo Gorge that Kingdon-Ward couldn't penetrate and discover if enlightenment could truly be found beyond the torrent of leeches. The result is a book that's exhaustively researched, wildly ambitious and occasionally impenetrable.

Baker wants to merge the styles of the two previous forms of Pemako-exploration accounts -- the literalist writings of British adventurers and the cryptic riddles of sacred scrolls -- in a single book. This makes "The Heart of the World" as much a primer in Buddhist doctrine as it is a travelogue. Tales of Baker's three major excursions into Pemako (in 1993, '95 and '98) are liberally intertwined with long digressions on esoteric Tantric doctrine and 19th-century expeditions.

It's hard to imagine a more thorough document -- the book explores Pemako's culture, geography and spirituality, often rendering the landscape in terms of local deities -- and Baker is probably the only man alive who could have written it with this much authority. "The Heart of the World" embraces the tension between spirit and flesh, and on that level, it's extraordinary.

Which is why it's sort of painful to report that Baker's prose style will lose a few readers en route to revealing Pemako's mysteries. There are straightforward passages of exploration that are cool and brutal -- but the author's devout spirituality also leads him to mythologize the world in sentences that can feel, on occasion, as if they had fallen out of a Buddhist version of the J. Peterman catalog. This is particularly true of the first third of the book, which chokes on such semiprecious introductions as, "I found Chatral Rinpoche sitting on the grass outside his hermitage feeding a consecrated tantric elixir to a flock of crows." (It doesn't sound bad taken on its own, but it's part of a cumulative annoyance.) And Baker's habit of thinking of elaborate, illustrative quotes at key dramatic moments feels a bit contrived by book's end.

Even worse are the thickets of doctrine so dense that you feel like a bit of an explorer yourself, passages such as: "According to the Guide of the Heart Center of the Great Sacred Land of Pemako: The All-Gathering Vajasattva Palace, a secret, black-bodied form of the wisdom goddess emanates from the center of the Kundu Lhatso with a retinue of dakinis while surrounding rock formations represent Padmasambhava in eight varying manifestations."

With all due respect to the Buddhist faith, Baker's eight-page glossary in the back of the book can barely extract the lay reader from that sort of quicksand.

Of course, that's unduly harsh. Baker fully intends to challenge your perceptions with that sort of prose, provided you're willing to take the journey. "The Heart of the World" is a book of faith and a book of exploration -- and a major departure from the traditional wilderness-adventure text.