(MONEY Magazine) – It was dark. Five-thirty-in-the-morning dark. But instead of slumbering in my Manhattan apartment, I was hustling out of my warm bed at the famed Rancho La Puerta spa for a 3 1/2-mile hike up a mountain in Mexico's rugged Baja California. (I really want to be here, I kept reminding myself.) After the trek and a spartan breakfast of oatmeal and juice, I went on to play tennis, lift weights and take a step aerobics class and a stretch class. Five hours of exercise--and it still wasn't lunchtime.

Welcome to the spa, late-'90s style. It resembles neither the deprivational fat farm of 10 years ago nor a European-type laze-about. On the contrary, the modern spa aims to whip men and women into physical shape and to soothe them mentally (and, of course, to leaven the mix with a judicious dose of loofah scrubs and aromatherapy facials). "Spas today are all about managing stress and becoming balanced," says Anne Harding, publisher of the quarterly magazine Spa ($14.85 a year; 800-835-2722).

That formula has struck a chord among the well-to-do but overstressed and out-of-balance boomers who make up the largest portion of spagoers. This year an estimated 250,000 Americans will visit either a so-called destination spa such as Rancho La Puerta (see the table on page B18 for eight top choices) or a spa attached to a resort hotel, such as Doral Saturnia in Miami. Fully a quarter of them will be men, up from 10% in 1987, says Frank van Putten, president of Spa-Finders (800-255-7727), a specialty travel agency in New York City and publisher of the annual guidebook Spa Finder ($5.95). And you don't have to be Imelda Marcos to visit one. Rates typically run from $1,000 to upwards of $4,000 a week--not exactly a bargain vacation but no worse than a week at a good ski resort.

I reckoned myself a near-perfect candidate for the spa experience (as I said wheedlingly to my editor). Like the average deskbound urbanite, I regularly eat on the run, get too little sleep and make it to the gym only half as often as I intend. After hearing glowing recommendations from friends, I chose the 57-year-old Ranch (as it's affectionately known), which charges a comparatively moderate $1,660 to $2,375 a week for a single guest.

When the shiny white bus that had picked me up at the San Diego airport an hour earlier rolled into the unlovely brewery town of Tecate, where the spa is located, I got a bit unhappy. But the Ranch itself is three miles--and a world away--from Tecate's seedy downtown. The spa sprawls over 3,000 acres nestled among Mount Kuchumaa's lush, boulder-strewn foothills, 3,800 feet above sea level. Gorgeously landscaped gardens abound with fragrant sage, lavender and rosemary.

The Ranch resembles nothing so much as a summer camp for adults. The Spanish colonial-style villas and haciendas that house the 150 guests are comfortable but rustic: no TVs and no telephones. Meals are served in an imposing red-brick dining hall where you share tables with other spagoers. Though only 20 men had come the week I was there, none I spoke to admitted to feeling the least bit uncomfortable. "I'll definitely come back," said Houstonian J.P. Bryan, 57, president of the Gulf Canada Resources oil company. "It's relaxed, and I can make my own schedule."

The Ranch offers so many activities, from aqua aerobics to yoga, that it's tough to be bored. Guests have the run of 10 gyms, four tennis courts, four hot tubs, three saunas, three swimming pools and a volleyball/basketball court. For serious hikers, there's the challenging four-day Extended Hiking Program, which culminates in a seven-hour, 10-mile climb up Mount Kuchumaa.

My days quickly fell into a routine of exertion in the morning and early afternoon, followed by pampering. While I've had better treatments, the nine I tried, from a 30-minute herbal wrap ($20) to an 80-minute facial ($60), were eminently relaxing. After a nightly massage ($40 for 50 minutes) to soothe aching muscles I didn't know I had, I promptly stumbled to bed.

If you can't do without your steak and cocktails, a spa is probably not for you. The organically grown Tex-Mex meals included no red meat or poultry (we had fish twice), no carbonated beverages, no alcohol and very little salt. Each guest gets a modest 1,300 or so calories a day and about 20 grams of fat. (If you're still hungry, though, the staff allows you seconds.) Starved for unhealthy fare, I escaped one night with a few other guests to a restaurant in town, where we inhaled carne asada and fishbowl-size margaritas (per-person cost: less than $20).

One other caveat: The isolation that makes the Ranch so wonderfully restorative can also make it frustrating to keep in contact with the office or home. To make an outside phone call, you must venture to one of 16 phone booths scattered around the property. Operators at the main desk will take phone messages, but you can't always count on their less than perfect English. "The first day, some people are huffy about it," concedes fitness director Phyllis Pilgrim. "But by the third day, they begin to think that maybe it's more important to go swimming than to get a fax." Perhaps that's the point.

By week's end, the place had won me over. My surefootedness and stamina on the mountain improved noticeably over those seven days. I felt, simply, healthy and energetic. And my clothes were hanging loosely when I returned home.

If you think a spa visit is for you, do your research early (one good guidebook: Fodor's Healthy Escapes, $17). You'll need to make reservations several months in advance. To hold down costs, consider traveling with a companion or in the off-season, which varies from spa to spa (it's mid-June through mid-September at Rancho La Puerta). Just think: This time next month, you could be casting off that workaday stress along a majestic hiking trail--or atop a soothing massage table.