It was a cool October night, and the sky, far from the city lights, was splattered with stars. But the brightest object in the heavens, aside from a three-quarter moon, was not a star at all, but the planet Jupiter. Through a telescope, I saw, with amazement, Jupiter and its four largest moons.

The sighting was part of a presentation by astronomer Michael Brewster, to which I had dragged my spa friend, Pam. And it was one of the sweet and unexpected pleasures of my return trip to the Lake Austin Spa Resort. My stay embraced spa essentials, such as yoga and massage, but also much more: cooking demonstrations, kayaking, cardio dance classes, a bit part in an A&E reality series, and, not least, new friendships.

It had been more than 13 years since I first visited the resort, on the shores of an artificial lake about 40 minutes from downtown Austin. Back then it had been a deeply charming place. The rooms were a bit rustic, the spa facility small. But the tranquil views, lush grounds, healthy a la carte cuisine, and casually relaxed atmosphere had suited me perfectly.

Since Mike McAdams and Billy Rucks, college buddies from Louisiana State University, took over the resort in January 1997 — just before my initial stay — the spa has undergone seemingly continual upgrading, including room renovations, two new pools, a lavish spa, a new gym, and the addition of a demonstration kitchen and garden library. The transformation has culminated in Lake Austin’s designation by Condé Nast Traveler readers as the top destination spa in the United States for the last two years. Unfortunately, its once-modest prices have skyrocketed along with its reputation.

My first visit to Lake Austin was in April, wildflower season, an enchanting time in the Texas Hill Country. But fall is also a good choice, with crisp, cool mornings and evenings and bright, sunny afternoons. Driving from downtown Austin, I was surprised by the development and traffic lining the road. Lake Austin no longer existed in splendid isolation.

But my welcome, once I passed through the gated entrance, was warm: I was immediately offered lunch. Not expecting that, I had brought my own so I settled outside, between the lake and the pool, to eat. After gulping down my sandwich, I ran inside for a culinary class with executive chef Terry Conlan. Conlan had been at the resort when I first visited, as had nutritionist Terry Shaw and some other staff members. Once at Lake Austin, no one seemed to want to leave. (Conlan retired this past March; his replacement, Stephane Beaucamp, has worked in Paris and Los Angeles restaurants.)

In the demonstration kitchen, I sat next to Pam, encouraged by her smile. She turned out to be an enthusiastic cook, as well as general manager at a Texas car dealership. Conlan served up portions of a delicate garden salad with toasted walnuts, olives, and pecorino Romano cheese; white bean soup with ham and smoked olive oil; and a spongy Cuban water bread. We finished up with chianti-poached prunes and vanilla frozen yogurt. Hunger clearly wouldn’t be a problem here.

My six-night package included a generous spa and fitness allowance and a Premier room. I chose one with a Japanese meditation garden, which I used mostly for drying bathing suits and checking e-mail. The room itself was compact, with a queen bed, terra cotta tile floors, a flat-screen TV, and a bathroom that looked out on my garden. A front porch afforded views of the spa’s organic herb and vegetable garden and, beyond it, the lake.

Every day offered different activities: exercise classes, hikes and cruises, talks on nutrition and stress management, even musical entertainment. I gravitated to yoga, cardio dance, and water aerobics, held in the Pool Barn — an indoor pool open at the sides to the warm autumn breezes. It was the resort’s only heated pool, and the only one designed for lap swimming; unfortunately, its temperature felt higher than optimal, at least for a Northerner.

One of the resort’s enduring charms is its intimacy, with just 40 rooms, and rarely more than 60 guests. It was less than half-full during my visit, so nothing was crowded, and water classes were particularly small. Even without pricey individual fitness sessions, I often found myself solo, chatting happily with the teacher as I bicycled across the pool. I recognized one water instructor, Sherri Dixon, who had given me private tennis lessons on my first trip, and I cherished our reunion.

The tennis courts, alas, were gone — razed to make way for the LakeHouse Spa, a 25,000-square-foot edifice ringed by gardens, fountains, the Pool Barn, and an outdoor pool. Guests await treatments or salon services poolside, or in the wood-paneled Blue Room, decorated with dried Texas flora and a tin chandelier. I booked a pedicure, a Swedish massage, and a Texas Starry Night, which featured lavender oil, massage, and body wrap. But my favorite treatment was the 80-minute Perfect Pomegranate, with a pomegranate scrub, shower, and pomegranate butter massage. For more relaxation, the locker room has a sauna, steam room, whirlpool, and private garden.

There is no structure at Lake Austin, not even a weigh-in. (I found a digital scale and weighed myself; in six days, I lost a respectable 4 pounds.) The new Power of 7 Program, begun last year, addresses this issue by customizing a schedule to help guests meet individual goals. For the rest of us, the toughest decision was where to curl up with a good book: A chaise longue by the spa pool, with ice water and a lavender-scented wash cloth? A plush chair in the garden library? Perhaps a hammock with a lake view?

Meals are similarly unstructured. Dining hours are generous. You can sit inside or outside, order as much or as little as you like. (Calorie and fat counts are listed.) Rushing to class? Grab organic oatmeal and fresh fruit from the breakfast bar. Or wait, sometimes too long, for exquisite (but tiny) lemon ricotta pancakes with raspberry syrup. Lunch included Southwest and Asian-influenced specialties: a smoked chicken quesadilla or a perhaps a Vietnamese vermicelli bowl, with shrimp, pork, and scallops.

Dinner is a social occasion, with up to five small-portioned courses: starters, soups, salads, entrees, and desserts. Apart from occasional misses, the food is fresh, light, and tasty. Wine is available, for an extra charge.

For those in search of conversation, there is a designated Friendship Table. I never found it, and the general conviviality of the resort made it superfluous.

I view my spa visits as a chance to experiment with the unfamiliar. At Lake Austin, I watched the sun rise as I did t’ai chi on the dock. I kayaked, exulting in the stillness and beauty of the lake — and the fact that I didn’t tip over. I tried Zumba, a Latin dance class, and something called Foam Roller Remedy. I went bird-watching, squinting through binoculars. And I shared a dance class with Ricky, who was being filmed for “Heavy,’’ a reality show airing on A&E. He was spending several months at Lake Austin on the cable network’s dime, an enviable fate.

Lake Austin has themed weeks, and my visit intersected with “The Culinary Experience’’ and a “Gathering of Wise Women,’’ featuring such topics such as “How to Be on Fire!’’ and “Dear Fear: Adios.’’ At one such session, life coach Debbie Phillips asked each guest to name the highlight of her spa experience. That was easy: I said it was the people I had met. Pam, sitting beside me, said it was the night that I had coaxed her outside to see the stars.