I KNEW I WAS IN TROUBLE when a graying, wrinkled man who could pass for my grandfather hiked past me. Then another person zipped by. And another. I was crawling my way up New Mexico's 12,481-foot Kachina Peak, skis slung over my shoulder, looking for fresh powder, but what I really needed was a stretcher. The mountain, and everyone on it, was kicking my butt. Not that I didn't deserve it—I'd fallen hard off the fitness wagon over the winter. But getting dusted by an octogenarian was more humiliation than my ego could stand. I needed a fitness intervention. "Call the Ranch," a friend suggested.

Rancho La Puerta Spa—"the Ranch" to those in the know—was North America's first fitness resort. It was founded in 1940 by Deborah and Edmond Szekely in Tecate, Mexico, just 75 minutes southeast of San Diego, and their vision has held steady ever since: Take a beautiful piece of high-desert land (in this case 3,000 rolling acres in the foothills of Mount Kuchumaa); plant it with lush bougainvillea, eucalyptus, and organic vegetable gardens; build Spanish colonial guest villas and state-of-the-art gyms; provide innovative exercise programs, an abundance of healthy food, and a dose of luxury; and you've got a recipe to save the world—or at least a worn-out blob like me. "This isn't a fat farm, it's a fitness resort," says 83-year-old cofounder Deborah, who swung by one night after dinner to greet guests. "I want healthy people to come here to get healthier and then go out and do good in the world. So get up and take a hike tomorrow morning."

At other spas I've visited, exercise means ambling to a lip-waxing appointment in a terry-cloth robe, and dinner consists of six snow peas and a few grains of brown rice. So when I arrived at the Ranch for a weeklong stay, I worried it wasn't the right place

The Ranch is like camp for adults, and everywhere I looked another taut body was buzzing away to a class or a hike, eyes locked on the long list of fitness options.

to get in shape—or, if it was, that I might starve in the process. My first night's dinner, a large plate of chiles rellenos (there is a spa god!), eased my apprehension; the rest of the week, I filled up on delicious Mexican-inspired cuisine, much of it grown in the resort's garden. And once I saw my fellow spa mates—an active, affluent, unpretentious group of about 120—my concern shifted to hoping I could keep up. The Ranch is like camp for adults, and everywhere I looked another taut body was buzzing away to a class or a hike, eyes locked on the lengthy schedule of daily fitness options. No spa sloths here.

The list of options starts with 6 a.m. hikes, and at any given hour thereafter you can choose from at least five different activities, from circuit training, cardio boxing, and boot-camp sessions to yoga and tai chi. Each morning, I went on the hardest hike available—five to seven miles at a brisk clip up the nearby mountain trails. (The Ranch also offers guided, all-day hikes in the surrounding region.) Then I bounced through the rest of the morning in a series of intense, expertly taught cardio classes.

My afternoons were about R&R. I attended lectures on nutritional and spiritual health, tried meditation, and lounged in the outdoor pools (there are three), hot tubs (five), and hammocks. But my favorite afternoon activity was a spa treatment at the colorfully tiled health center, where I indulged in a sports massage, herbal wraps (lying rolled up in steaming, herb-soaked sheets for 30 minutes—excellent therapy for aching muscles), and a hot-river-stone massage. One day I booked back-to-back massages and emerged two hours later in a state of altered consciousness.

I was transformed by six days of this routine—my body sprouted muscles I hadn't seen since college sports. Best of all, back home I stayed energized enough to exercise regularly, which I've been doing ever since. Look out, Kachina Peak—at least all the elderly gentlemen on it: I'll be back.

Access & Resources
Details: $2,460–$3,725 per person per week, including meals, all fitness activities, airport transfers, and non-alcoholic beverages; 800-443-7565, www.rancholapuerta.com