On the morning we broke camp, the weather also broke, and a warm, summery breeze blew. Our caravan trailed across lush meadows and along pebble-strewn beaches, through larch stands where brown snowshoe hares leapt away in the spattered light, and then out along packed, unobstructed lakeshore tracks that stretched out of sight. That afternoon we detoured along a little-used horse-and-goat trail. Peter called it a "shortcut" to the town of Hatgal—with 300 residents, the biggest village on the lake.

Some shortcut. The trail cut across soggy wetlands and then rose sharply to a dramatic ledge, with singletrack lacing sheer 100-yard drops to shallow, rocky, windswept lagoons. At one turn I snagged my pedal on a stump and flew forward, far out over my handlebars, catching air—big air. My bike and I plunged through tangled brush and down a slope that led to a cliff. Fortunately, I came to a stop well before the edge, and suffering nothing worse than a chainring track snaking down the back of my thigh.

A few miles later, we crossed the Egiyn River on a weathered bridge. On the other side, smoke rose through a tattered tepee where a woman was brewing "brick" tea, which is dried in the shape of a brick and then broken off and ground before it's steeped and diluted with reindeer milk. She served it with a plate of hard biscuits and even harder cubes of reindeer cheese. She was a Tsaatan, one of the "reindeer people," the most restless of the nomadic herders (they move at least ten times per year), whose dwindling 17 families live mainly in the border area between Siberia and Mongolia, west of Lake Khovsgal. This ruddy-faced, expressive woman, her watchful, silent husband, and their children have learned to track the tourists who visit the region. They'd gotten word of our trek and had traveled southeast to intercept us by camping on our probable route. Courtesy dictates that you stop and pay a visit.

We were happy to. They presented a perfected routine—a visiting session in the tent, rides on a few listless reindeer, and as many photographs as we could want, all for about 4,000 tugrog, or $4, for our whole group. As we departed, the family's teenage son rode up on a reindeer, its fuzzy rack of antlers almost bigger than he. Spying our bikes, he jumped off his mount and enthusiastically accepted Bold's offer of a teetering spin on a bike.

We spent four more days roaming the Harhuth Valley, looking for golden eagles and listening to wolves that howled in the night. But that perfect day—when we visited the Tsaatan, then took off through mud to Hatgal, and arrived exhausted to find the ever-reliable Maagi whipping up plates of mutton and fried rice—must've been the clincher in convincing Boojum to do it all again next month.

Born in China, writer Martha Sutro now lives in Missoula, Montana.