But the trip sounded interesting, and a voluntour was a chance to connect with my son before he left the nest for good. A rock and roller who grew up in Asia but now lives in Brooklyn, Oliver sleeps until 2 p.m. when he can and considers moving band equipment aerobic exercise. A Peruvian farm would certainly shake him out of his comfort zone. How would he cope, far from computers, phones, and friends? And how would we get along? I bought us both long underwear, rain ponchos, and granola bars, and off we went.

In Lima, we toured the Iglesia San Francisco, where the bones of thousands are ghoulishly displayed in the crypts, then lunched on perfect seviche near the beach before meeting our guide José Bastante, a Peruvian archaeologist, and Kim, an Australian teacher. The next day, we flew to Cajamarca, where in 1532 Atahualpa, the last Incan emperor, made his final, disastrous stand against Francisco Pizarro. The colonial town was bustling with commercial activity: Women in full skirts and tall straw hats sold candy and T-shirts on the narrow streets. We stopped in the Iglesia Belén, a Baroque church with oversized, large-breasted angels peering down from the ceiling, and sloshed around the next morning at the hot springs outside town, where family groups come to bathe.

A six-hour bus ride later—with a midday stop at a shack with no electricity, where the other passengers cheerfully ate rice and chicken in the dark—we piled into a truck for another hour's drive into the hills. It occurred to me that the journey itself was an important part of our experience—moving, literally, into another world where things happen at a different pace. Finally, a walk up a muddy path took us to the Blue Poncho Lodge, which has several simple bedrooms and a kitchen. A heavy rainstorm had blown a fuse, so Celia, the cook, served us spaghetti by the light of gas lamps.

We awoke to a bright highlands sun slicing across green farmlands that stretched up the hillsides, dotted with cows and the occasional horse. A hummingbird fluttered next to some red flowers in the garden. Mercedes, the local program officer, showed us how to make chimneys, flattening large strips of corrugated aluminum with wooden bars. Amazed, I watched Oliver throw his shoulders into the job.

The next day, we headed up the hill to the two houses for which we were building the stoves. Panting as we climbed a muddy path blocked by boulders, I watched Oliver clamber ahead. After a farmer on a mule tentatively made his way down the slippery path, I suggested out loud that a road might vastly improve these people's lives. Oliver retorted angrily that I was a snob: A road might actually spoil their lives. Wasn't that cultural arrogance? I thought. It seemed an easy assumption to make, since we have all the roads we could want. I decided to ask the farmers.

When foreign volunteers first came to Cadmalca, the locals thought that the gringos must have found gold. After all, for centuries precious metals were all foreigners—first the Spanish conquistadors, and then the American mining companies—ever seemed to want. But the program's founder established a small tour operation with sustainable goals: The visitors' fees would cover the cost of employing a few farmers part-time, and one by one, families would get stoves. The women would no longer have to suffer chronic respiratory problems.