The old Wakhi horseman sucks deeply on his pipe, the opium glowing scarlet in the darkness, and blows smoke in my face. We're lying side by side on pounded wool mats in a cavelike hut in far northeastern Afghanistan. The stone walls and stick ceiling drip with black tar from decades of burning yak dung. A goat is butting its horns against the crooked door. Outside, the sheep are shu¤ling nervously inside the stone corral, waiting for a wolf to take one of them.

The fire is almost out and everyone is asleep—pressed together for warmth like the animals—except the horseman and me. His wind-shot eyes are shut. He inhales, his craggy face relaxing, then exhales, the psychoactive smoke swirling around my head.

Another long day done. Our team of eight—three Americans, our Pakistani guide, and four Wakhi horsemen—is walking the Wakhan Corridor, Afghanistan's ancient, forgotten passageway to China. We are more than halfway through, en route to Tajikistan. Marco Polo passed this way 734 years ago. It was medieval then, and it still is.

It was late afternoon today when we climbed out of the dark canyons up onto the treeless, 13,000-foot steppe. Two vultures, with their pterodactyl-like six-foot wingspans, were circling above a yak carcass. Our day's destination, a place called Langar, turned out to be this solitary hut out on the vast brown plain. A gaunt woman in a maroon shawl invited us into the smoke-choked shelter and gave us salt tea in a chipped china cup. Her name was Khan Bibi. She was 35, but she was weather-beaten and missing teeth and looked twice her age. She began making flatbread, wetting handfuls of flour with water from a pail. She sent her youngest child, a four-year-old girl whose nose was running with green snot, out to collect disks of fuel. With blackened hands the woman slapped the slabs of dough against the horseshoe curve of the clay hearth. As they finished baking and fell off into the fire, she reached into the flames and passed them to us.

We all went back outside when we heard a chorus of baaing. Khan Bibi's husband, Mohammad Kosum, 45, and their seven-year-old son, both in black Russian fur caps with earflaps, were bringing the sheep and goats into the corral. Together this family of four began lifting lambs and kids from a cellar, placing them with their correct mothers, allowing them to suckle, then dropping them back down into the two-foot-deep hole where their combined body warmth would keep them alive. With 800 animals to move, the process lasted till dark.

Khan Bibi returned to the hearth and squatted there for the next three hours, making us rice and more flatbread and more salt tea. There was no electricity, no lamp, no candle. Dim orange firelight and a shaft of blue moonlight cut down through the whirling smoke from a square hole in the roof. The tiny girl fetched water from a snowmelt creek that runs through the reeking carcasses of yaks that died during the snowy spring. When we were all fed, Khan Bibi curled up on the shelf above the fire with her two children and pulled a yak-hair blanket over the three of them.

Now, hours later, the old horseman is next to me, blowing smoke in my face. He's on his fourth or fifth bowl. I can't keep track anymore. I'm floating on secondhand smoke, back to my first day in Afghanistan.

I'm running up Aliabad, a mountain in the middle of Kabul. Tilting dirt streets with runnels carved down the middle by sewage. I pass two faceless women, heads trapped inside helmets of blue mesh. In the rocks above the flat roofs, I pass a shepherd girl shooing sheep along the mountainside. I reach the top and begin to run along the ridgetop in pink light. Up and down through trenches, stepping on piles of rusty four-inch-long bullet casings, skirting a blown-apart artillery gun, leaping an ordnance dump.