AT KAILAS, WE LEFT the tourist route, heading north where the others turned east, back toward Lhasa. Our journey had barely begun. For days we rolled through long valleys, over the soda plains of highest, remotest Tibet, toward the Kunlun Shan, where the plateau fell into China's Central Asian deserts. Between us and paradise lay the Aksai Chin, one of the least-known places on earth, an immense and uninhabited grassland at 11,000 feet. Nanda Devi, at 25,645 feet, shone brilliant white, perhaps 60 miles away. We passed K2, hidden by closer peaks. The view was still impressive, a sky-long chain of jagged mountains under a perfect blue heaven. Pay no attention to those who say the world is shrinking.

The Aksai Chin is a closed military zone. Still claimed by India, the territory is firmly in Chinese control, as we discovered one snowbound dawn when military police in Chinese jeeps shoved us off the road. An entire Chinese infantry division appeared: 3,000 or more men, brilliantly equipped, in a convoy of 300 trucks, pulling howitzers and antiaircraft guns, and escorted front and back by scores of SUVs containing suspicious officers. This was the Xinjiang Division, according to our stalwart driver, a careful Tibetan who knew full well that we were reporting without press visas (and wisely insisted on anonymity). For the next two days we tangled with this army convoy, passing parts of it, getting turned back, overtaking it again, driving through open desert to flank the troops, and then being turned back yet again. Finally we caught the entire convoy eating lunch and, relying on our store of merit and blazing smiles, drove right through a host of screaming MPs.

The days on the Aksai Chin were indistinguishable, a stream of 16-hour road marathons, sudden whiteouts, and 2 A.M. negotiations with truck drivers over towing fees. We were rubbed raw and lean, feeling that curious mixture of numbness and heightened senses, of discomfort and revelation, that causes you to value a single sunset while traveling—a final narrow ribbon of blood orange, dividing a black range of peaks from the dark night above—more than all the sunsets you have known at home. With life reduced to transitory essentials, we approached the state of mind of the old caravan routes, close enough to smell the camels, able to glimpse something of the ancient and alien journey laid out by Rinpungpa and others.

To get to Shambhala you still have a long road ahead ...

Ed Bernbaum argued convincingly that the Kunlun Shan could be the "outer ring" of snow mountains that conceal Shambhala, the last barrier to the great desert mentioned in texts. Shambhala is also round, like this desert region, wrapped in a "circle" of ranges (the Kunlun Shan, the Tain Shan, and the Pamirs) that contained scores of Silk Road principalities, some of them specifically identified in the guides.

Home was now closer ahead than behind: After more than 2,000 miles of travel, the Kunlun Shan was the dividing point. It was my 41st day on the road, and we followed switchbacks up and down, through valleys no wider than a Frisbee toss, until we slipped beneath a great pendant mass of black rock covered with a scabbard of white snow, a terrible and despairing sight, even with a road to guide us through. It was hard to take such a mountain as mere metaphor, a symbol of some interior peak of the soul.

Whatever our difficulties in coming this far, they paled to nothing by historical standards. The Kunlun parted for the Toyota, hour by hour; all this road required was patience. We crossed three ranges and then, just as abruptly as we had climbed up onto the Tibetan Plateau, we fell off it. Between two peaks, I saw a long, brutal vista of endless waves of dunes, each giving off a snake of sand to the fierce winds. This was the Taklimakan, the western extension of the Gobi and by reputation the fiercest desert on earth. It wasn't an idle reputation: Eighteen years before, I'd spent a hot month here with a Danish woman, scouring archaeological sites. The heat, the electrified dust storms, all the bad food and rough travel, the skin-cracking aridity of the Taklimakan, had been bearable only because I was blindly in love. In Uighur, the language of the Muslims here, Taklimakan means "Go in, don't come out." Everything I loathed in a 1,000-mile package.

At a leafy village full of white-capped Muslims, we crossed an internal border post. The snarling Han Chinese policeman was so busy mistreating the Tibetan truck drivers that he passed us into the Xinjiang Uygur region without a second look. At dusk, out on the plains, we saw the first oil rigs, topped by flaming beacons, and wove the Land Cruiser through our first herd of camels. These were double-humped Bactrian, Silk Road beasts with summer coats and clear eyes. The temperature had risen 40 degrees.

In the Tengyur guide, the oldest of all Tibetan sources on Shambhala, you are advised at this point to join a caravan to continue north. Writing eight centuries later, the third Panchen Lama warned: You will cross a place without water or people ... It is desert ... go for 21 days.

But we could go nowhere. For ten days, Seamus and I were entangled in the infamous Middle Kingdom bureaucracy, trying to extend our now violated visas. In Yecheng they said only Hotan could approve such things; in Hotan, Yutian; in Yutian, Korla. In three cases, we were denied an extension for a group visa by police officers standing beneath signs reading, in both English and Chinese, EXTENSION OF GROUP VISA 50 YUAN. In the welter of miscommunication, frustration, and freezing-cold police stations, I lost my sense of humor. ("SEAMUS!" I caught myself screaming at one point. "I. AM. TRYING. TO. SPEAK. CHI. NESE. GO. SIT. IN. THE. CAR.")

The 13th-century lama Manlungpa had passed through the Kingdom of Li, famous for its jade. That was not hard to identify: The ancient jade markets of India, Nepal, and Tibet were all supplied by a single source, a riverbed outside modern Hotan. Mud walls were all that remained of Li, but hundreds of men, mostly Uighurs, were still working the riverbed for jade. They are the descendants of the Paksik mentioned by Rinpungpa, the horsemen in quilted cotton jackets and white turbans. The Uighurs have seen better days: Today they face much of the same religious and economic isolation as Tibetans, without the romantic figure of a Dalai Lama to give them a voice abroad. But in the first millennium, when they practiced Buddhism, they built the Silk Road into a wealthy and powerful network of trading oases and uncountable monasteries, where Buddhism, but also Christianity, Taoism, Islam, Manichaeism, and Zoroastrianism, were debated, studied, and transcribed into new languages. The Kalachakra teachings reflect knowledge of all these faiths.

With only two days left on our visa, we hired a taxi to sprint north, to Urumqi, the capital of Xinjiang. The road was new, built by oil companies since my 1980s visit, and the fearsome Taklimakan yielded in 11 hours, not 21 days. It was a featureless wasteland, a hopeless ocean of heat that finally descended, on its northern edge, to marshland, and then the great cleaving river, the Tarim.

If the Kunlun Shan doesn't look to you like the "outer ring" of snow mountains, and the jade kingdom of Li leaves you unconvinced, and the circular shape of this desert basin doesn't reflect the lotus-like geography of Shambhala, and you somehow doubt the Taklimakan is the great spiritual desert that pilgrims must cross, still you must acknowledge the river. In all ancient accounts, the river that protects Shambhala flows east; the Tarim is the only major river in Central Asia that flows east. Wherever the kingdom lay, it was somewhere north of this river. We now left behind all maps.