(FORTUNE Small Business) – There's something not quite right about the phrase "luxury hiking." Hoofing it through woods and up canyon trails is an unavoidably sweaty proposition, and the toilet "behind that big rock" is hardly five-star. But what if you could take guided group hikes during the day and sleep in upscale hotels at night? Dine on so much ahi tuna, lobster, and steak tartare that you'd beg for a simple salad? If your idea of roughing it is a Hilton, but you want the serenity of nature and the vigor of a hike, an active travel vacation might be for you.

Berkeley-based Backroads is one of the most popular companies to offer such trips, with 13,000 customers a year. In 2004, Travel & Leisure rated Backroads the No. 6 tour operator--of any kind--in the world, based on the quality of its excursions. This year it has added 14 new hiking options, including China/Tibet and Czech Republic/Austria, though about a third of the firm's 35 walking tours are in scenic parts of the U.S. Its bookings on walking trips are up 30% compared with last year, possibly a rebound from the travel industry's slump after 9/11. (For other companies offering such trips, please see the box that accompanies this story.) Helen Nodland, a travel-agent-turned-marketing-consultant who has worked in active travel for 20 years, pegs the growth to the baby-boomer demographic. "Younger people will backpack and then settle down with kids and a house," she says. "Fifteen years go by, and suddenly they're 45 and looking to travel again. They have less time and more money, and like to stay in shape."

I chose a Backroads hike in the Southwest, which cost $2,298 for six days and five nights in Santa Fe and Taos, N.M. That included hotels, transportation, and nearly all meals--basically everything but airfare. (Industrywide most prices range from $1,000 to $6,000 a week.) If you go on vacation to avoid small talk, this is not for you--most active travel is done in groups of about 20, plus two guides. Everyone hikes together, eats together, and stays at the same hotels. In one week I was prodded for my life story at least six times and had no more than three hours a day to myself. That one-big-happy-family approach is why the trips are popular among women, especially women traveling alone. Across all its trips, Backroads says, 54% of its customers are women; on mine, it was 75%.

On our first day we gathered in a Santa Fe hotel lobby. The group ranged in age from 27 (me) to 69, with the majority in their mid-40s to mid-50s. The brochure told us that we would be hiking from 1.5 miles to eight miles a day, and many of us were nervous about how tough the terrain would be. The brochure also recommended that we "walk or hike at least three times a week and for at least one hour on each outing" in advance of the trip, but I had been too busy. The youngest in the group, I figured that if I ran out of energy, I would let shame propel me up the hill.

Our guides, Tim Nenninger, 38, and Annie Girard, 30, showed up at 9 A.M. and loaded our luggage into their trailer, towed by one of the two 15-passenger vans that would carry us to and from our hikes. (Unlike some inn-to-inn hiking options, particularly in Europe, Backroads trips don't involve walking to the inns each day; instead there's a fair amount of van travel to and from the trailheads.) Becoming a Backroads guide is more competitive than you'd think: Thousands apply each year for about 80 slots. They're chosen less on physical fitness--a given in this group--than on social skills and leadership. Once selected, they go through a three-week training course, shadowing veteran guides and learning CPR and first aid and, of course, how to drive those big vans. Both Tim and Annie could identify any bird that flew by, explain the life cycle of a piñon tree, and recommend coffee shops in Taos.

The first day's hike was at Bandelier National Monument, a 1.6-mile warmup to help us adjust to being 7,000 feet above sea level. As we explored the Tsankawi ruins, cave dwellings inhabited by the Anasazi tribe until about the 1500s (all the hikes on my trip offered points of cultural or geographic interest), I could feel my heart thump against my rib cage, which strained to pull enough oxygen from the thinner air. Even the gym worshipers among us were stopping to catch their breath.

The idea of outdoor athletics as guided vacation came about roughly 25 years ago, with a handful of small companies offering mostly biking trips. The founder and president of Backroads, Tom Hale, now 52, was one of the first: In 1979 he had the idea of taking vacationers on bike rides throughout the West. It wasn't until 1992 that his company began to offer walking trips. Today, like many of its competitors, it operates on six continents and offers several variations on the theme: family trips, singles trips, "easy explorations" that involve hikes of less than five miles a day, or "epic journeys" (e.g., cycling the Tour de France course). This year Backroads launched Casual Inn vacations, which replace five-star accommodations with three-star and cost 20% to 35% less. While hiking and biking are the most popular categories, adventure-travel companies also offer guided adventures in bird watching, canoeing, kayaking, hot-air ballooning, and even in-line skating. Most of the trips involve some local culture: In Italy you can bike past Renaissance churches; in Cambodia, you tour the Angkor Wat temple.

And then, of course, there's the food. The unwritten rule of Backroads trips seems to be: Keep eating. From the post-hike picnic lunch, to the fruit basket in the van, to the lemon bars and buttery shortbread that awaited us at our first inn, to a three-course dinner that night, Tim and Annie made it impossible to go hungry. At restaurants we could order anything we wanted from the menu, though we had to pay for our own alcohol.

The hike on day two was a 6.7-miler along the Rio Grande Gorge, beginning with an 800-foot descent--a knee-and-ankle-crunching series of switchbacks. Backroads offers walking sticks, and they were useful to avoid sliding. But when we hit the uphills I started to feel the altitude. Even pausing every 30 seconds to catch my breath, I still wondered if I could have a heart attack before age 30. "Am I as red as you look?" I panted to the man next to me. He nodded, breathing with his mouth agape. The last two miles were blessedly flat fields of volcanic basalt. There's a fine line between a feeling of accomplishment and "Thank God that's over." I was somewhere between the two.

Never on this trip did I set foot in a sub-$250 hotel room. Backroads scouts all the top places in a region before selecting the inns where it puts up its guests. Every night was luxurious, but the lodgings on night three stood out. Rancho de San Juan, in the desert outside Española, N.M., is the only hotel in the Southwest belonging to the prestigious Relais & Châteaux organization. It has five bungalows, or casitas, each positioned to provide desert views with no other buildings or people in sight. Mine normally is $425 a night, and I could see why. The view from the wall of windows in my living room was so stunning that I left my bedroom unused and slept on the living-room couch in order to wake up to the sun rising over the mountains.

Hotel owners (and life partners) David Heath, 63, and John Johnson, 59, opened Rancho de San Juan in 1994 after 35 years of vacationing in the area. Rancho's restaurant has been named No. 1 in New Mexico by the Zagat survey every year since 2000. Johnson, head chef until recently, ceded his toque to 30-year-old Chris Rocha, who started us off with a lemongrass and shiitake mushroom hot-and-sour soup. I found myself wishing for more, despite not having felt a pang of hunger for three days. About halfway through the entrée, a choice of swordfish (my selection, with tomato-almond coulis) or lamb, my stomach hit the wall. I couldn't possibly eat any more. "Thank you," I said weakly as the waitress delivered my Maui pineapple marzipan upside-down cake. "Just one bite." I all but licked the custom-printed Limoges plate.

By day five I'd had almost enough hiking. All along Tim and Annie had encouraged us to skip any hike we felt was too much, but only now did two vacationers in the group opt out. In the name of rigorous reporting, however, I stumbled the four miles up and back, a slack-jawed mouth-breather, leaning heavily on my walking stick. The hike began at 10,000 feet--above which altitude sickness becomes a concern--and went up to 11,400 feet, where snow was falling. When I collapsed in the van, I knew that once I'd showered and rested, I would look back on my vacation with a feeling of accomplishment.

Of course there was still one last meal, a farewell lunch consisting of a chile-pepper cheeseburger, chicken and gorgonzola tart, or ratatouille panini. "Is there dessert?" I asked Tim, fearful of an affirmative. "No, but we could get you some if you want," he said. "No!" I told him. I had become stronger in more ways than one.