It was 12:45 a.m. when I pulled off Highway 1 in Big Sur, Calif., and joined a half-dozen couples and small groups of friends waiting quietly in rental cars under a twinkling black horizon. Was that a shooting star? The breeze was redolent of redwoods and sea salt, and the surf sounded rhythmically below like the soft breath of children, already asleep.

But where was the moon? I had chosen this night to visit the Esalen Institute, a remarkable center of American cultural experimentation for the last half-century, because of the promise of the full moon.

I remembered it vividly from my last after-midnight visits in the mid-1970s, and I had checked online from my Super 8 Motel in Monterey before setting out on a dark, insanely twisting, 90-minute drive to this spot over the Pacific.

The moon should be full. But where was it?

Moments later, we were out of our cars and facing west across the churning Pacific Ocean toward Asia, as Esalen has always enticed people to do in religion, philosophy and psychology.

Then it dawned on me. The moon was behind our backs. Suddenly it emerged over the black brim of the Santa Lucia Mountains, a verdant geological wall that separates Big Sur from all points east. It was a fitting reintroduction to Esalen, a remote cliffside place at the extreme western edge of North America that has always altered the perceptions, if only temporarily, of those who enter.

Now in its 52nd year, few destinations have attracted such a boundary-challenging group of artists, seekers and intellectuals. Joan Baez composed music from a cabin on the Esalen grounds, Timothy Leary was a resident master of mind-altering drugs, Alan Watts and Joseph Campbell were scholars in residence, and Hunter S. Thompson was fired as a security guard.

But while Esalen gained a global reputation in the 1960s and 1970s as a center of counterculture and the “human potential movement,” a simpler tradition was taking hold after midnight in its spring-fed hot sulfur baths.

The baths have always been Esalen’s raison d’être. Thousands of people book lodging on its grounds each year to attend workshops on massage, yoga, Eastern religious practices, holistic medicine and the arts, and for these visitors, the baths are a place to meditate, socialize or simply gaze over the Pacific.

Clothing is optional, and many choose to wear nothing.

The experience has lost none of its capacity to unsettle and inspire.

At 12:55 a.m., a man from Esalen greeted us at the Highway 1 entrance. After boarding a golf cart-like vehicle, we were driven down a sharp grade into the institute’s assemblage of lodging, work rooms and exercise spaces. The group was limited to 20, and we had all made reservations.

Esalen accepts reservations for after-midnight bathing only over the phone. From May through October reservations are accepted up to six weeks in advance, but from November through April, when harsh weather can place the baths off-limits, only same-day reservations are accepted.

We had come from England, New York, Colorado and other locales across the United States. We were limited to two hours in the baths.

By now, the moon was in full bloom over the Pacific. Perhaps inevitably, one’s inclination upon walking into the Esalen baths is a mix of introspection (What I am doing here with a bunch of strangers?) and sheer wonder at the natural setting.

We walked down a stairway into immaculately clean coed changing areas, with showers. Esalen provides towels. In the dark, it was difficult to discern how many visitors were naked before entering the baths.

There are seven sulfur baths, all fewer than 100 feet above the churning, kelp-congested surf. Several couples in my group found private corners, but visitors are free to roam.

The bath that I chose was open to the night sky, surf and the faint scent of beached kelp between ancient boulders. I climbed in reluctantly, and almost blindly, to join three other bathers whom I had never met. Their faces were obscured by darkness and steam.

Lindsay Kloberg and Erin Hess, both 26-year-old schoolteachers from Milwaukee, were on a three-week cross-country escape.

“I’m surprised that a place like this actually exists,” said Kloberg, who teaches high school English. The experience, she said, was “surreal and meditative.”

Gerardo Herrera, a 47-year-old Los Angeles designer and a frequent participant in Esalen workshops, was also among my chatty cohort in the steaming tub. He and his wife had booked a room on the grounds, where they were attending a workshop, and he had elected to stay up late.

After midnight, he said, the atmosphere was different.

“To come at this hour, you have to have an open mind,” he said. “Even if people are modest, I think, they tend to open up.”

“Maybe it’s the darkness,” Herrera added. “It can bring out the social side of people.”