Everyone smiles as you drift past the flowers/ That grow so incredibly high.

— “Lucy in the Sky With Diamonds” The Beatles

Picture yourself in a room by an ocean with pink-petaled trees and sapphire skies. Then imagine being surrounded by guides feeding you a powerful hallucinogen every 72 hours or so, to expand your consciousness and strip you of your ego “game.”

For two summers in 1962 and 1963, at least 50 day-trippers retreated to the Hotel Catalina Beach Resort on the Pacific Coast in Zihuatanejo, Mexico, to do exactly that. The first known Western psychedelic retreat was organized by the soon-to-be-fired Harvard psychology professor Timothy Leary and his partner in mind-expansion studies, Richard Alpert (renamed Ram Dass after a visit to the Himalayas). They called themselves the International Foundation for Internal Freedom — IFIF.

Leary would soon come to be known as a leading apostle of psychedelic drugs, and for a time this little beach resort accommodated tripping acolytes under his insouciant tutelage.

Today, the Catalina is the oldest resort in Zihuatanejo. The city now has dozens of hotels and villas, many Mexican-owned, yet it still feels like the anti-Tulum. The laid-back beach city does not have the gloss and overdevelopment of that Yucatán Peninsula town.

Direct flights arrive at the nearby airport from American cities, including Houston, but Zihuatanejo and its environs are still sleepy enough to host four species of nesting turtles. Locally grown vanilla, coffee and sea salt are on offer at market stalls, and outdoor cafes sell caffeine concoctions at a fraction of Starbucks prices. Foodies are attracted to a growing number of restaurants serving up fresh seafood innovations.

Even with the rise of interest in therapeutic psychedelic drugs, most visitors in Zihuatanejo come for sun and sand, whale watching and to participate in the popular baby sea turtle releases. They are likely unaware of resort city’s storied past with Leary and his 1960s experiments in consciousness expansion.

Nearly all the IFIF participants have died, and the only telltale sign of that ecstatic time is the Catalina hotel, standing at the center of a crescent of sand called the Playa la Ropa.

Its owner is the stepson of the man who leased the hotel to the IFIF. Alexander Bergtold doesn’t remember the IFIF retreat, but recalls that when he was a boy, the town was so rugged it took him an hour to walk to school from the hotel grounds. “It was an absolute retreat for them,” Mr. Bergtold said.

The resort has three times more bungalows now, but the jungle vibe is unchanged. A pheasant-like bird called the chachalaca still perches on the Mexican plumeria tree with its delicate white blossoms. Black darts of pelicans aim at fish in the waves. Night and day, the rhythmic slap of water on sand lulls the mind into a meditative state.

Tuning out and tuning in

The IFIF Psychedelic Training Center’s goal was ambitious. A group of psychologists, graduate students (mostly male, plus wives and girlfriends), the occasional actress, businessman and curious interloper would sequester in a paradisal place, tune out mushroom-cloud-haunted, midcentury America, and tune in to an expanded consciousness they believed was once the province of shamans, prophets and participants in the Eleusinian mysteries, the best-known secret rituals in ancient Greece.

During World War II, LSD was discovered by a Swiss chemist who hallucinated for hours after a drop from one of his experiments got on his skin. In the late 1950s, the C.I.A. was testing it as a potential mind control weapon while psychiatrists were experimenting with its potential as therapy for mental illness and alcoholism. By the time Leary came to it, the class of drugs, including psilocybin mushrooms, had also gained popularity among literati, including the 20th-century British writers Aldous Huxley and Alan Watts.

The drugs could induce psychosis, especially in people who underwent clinical tests strapped to metal beds under harsh lights. But Leary and his allies and acolytes believed that hallucinogens could work as therapy if “set and setting” were carefully managed.

Zihuatanejo appeared to be an ideal setting in the ’60s. Then a tiny fishing village, 150 miles north of Acapulco, it could take 14 hours to travel by air from New York or Los Angeles. There were no direct flights or paved roads. Homes were lit with kerosene. The only hotel in town, the Catalina, had a single four-wheel drive truck to ferry guests up and down the muddy path to and from the airport. The beach below was a thoroughfare for fishermen, farmers with loaded burros, children and dogs, going from one end of town to the other.

Leary easily persuaded the Catalina’s owner to lease the whole place to the Americans for the summer, which is low season for tourists. They christened it the Freedom Center and charged participants — selected from a reported 5,000 applicants — $200 for a month’s room and board.

Arrivals were handed the following instructions: “The aim of the transpersonative community is to liberate members from their webs so that they can soar, at will, through the infinite space of their consciousness or throughout the infinite time/space of the energy fields surrounding them. IFIF has come 4000 miles to get away from YOU! You may be frustrated to find people here who are uninterested in playing the game of YOU. Don’t feel hurt. Climb out of your web and float after them.”

The California psychiatrist Joseph D. Downing spent two weeks with the group and left behind the most scientific assessment of the operation. He concluded that the drug improved neuroses faster than psychoanalysis.

Participants were fortified before their so-called ego deaths (which Leary and Co. defined as a drug-induced separation from reality) by reading Leary’s adaptation of “The Tibetan Book of the Dead.” There was, of course, a brutality to it — the stripping of the ego could bring on “bad trips” and lasting mental health issues. But the goal was psychic rebirth. The “sacrament” was powerful, pure lysergic acid diethylamide, LSD-25, administered by the leaders in varying doses. The group leaders hid the LSD in a glass container out in the bay, under water.

All drug ingestions were to be overseen by guides. But often those guides were tripping themselves — one of many scientific taboos that ultimately provoked Leary’s expulsion from the academic community.

Among the few living participants of the IFIF experiment, Gunther Weil, 85, a psychologist and management and leadership consultant, recalls it vividly. “The Catalina was a 24-7 olfactory sensory experience,” he said. “I once saw a plant grow overnight.”

Aztec symbolism and traditions added a layer of exotic appeal to the minds of these upper middle class trippers. Leary waxed lyrical when recounting a Mexico LSD session in his memoir, “High Priest.” As the drug took hold he wrote that he became aware of the jungle as “a dark unyielding valley … ”

Today, the view of the cultivated tropical garden from a high terrace at the Catalina is essentially unchanged. Blackbirds and cuckoos shimmer in the bougainvillea and hibiscus. Hummingbirds, believed by the ancient Aztecs to carry the souls of babies who died, feed at the blossoms.

Trouble in paradise

Mr. Weil remembers that the central goal was creating a community to go forth and remake human psychology, a reset deemed necessary at the dawn of the atomic age. And in those paradisal environs, the drug enhanced a sense of the possible.

It wouldn’t be paradise without ejection, of course. IFIF was not destined to last through its second summer.

Leary never tried to hide his project from the Mexicans or the Americans. He invited major American media to visit, even after Harvard fired him for failing to attend his scheduled lectures. Press coverage of the retreat was skeptical at best.

Their Mexican neighbors were bemused. The Zihuatanejo historian Rodrigo Campus Aburto, a young teen in the 1960s, recalls that the community thought the mostly American trippers were lunatics. He also remembers older teens sometimes attended fiestas that IFIF hosted on the beach. “Moon, fire and beer,” is how he describes the parties. Some smoked marijuana (Guerrero state was then, and still is, a major marijuana producing area), but “the sacrament,” as the IFIF people called their LSD, was not shared with the locals.

It was decades before the rise of the narco-trafficking that has wreaked murderous violence and havoc on Mexico. The one rule of IFIF was that people on LSD were not to leave the compound, and by all available accounts, that seems to have been followed.

One or two individuals did wind up in Mexico City hospitals with breakdowns, according to a Saturday Evening Post article published in the fall of 1963, titled “Mind-Distorting Drugs: The Weird Saga of LSD.”

On June 13, 1963, the Mexican government formally gave the group 20 days to leave the country. It’s unclear exactly what prompted the expulsion. “They were breaking the law,” Mr. Aburto said. The Saturday Evening Post reported Leary got the group deported after he read a paper on LSD at the National Autonomous University of Mexico’s Institute of Biomedical Research, as it is now known. The scandalized director deemed his talk “absurd, confused, valueless,” and protested to the Mexican government.

Besides the Mexican federales, the group faced a more primeval challenge. The group was 60 percent male, and Dr. Downing, the California psychiatrist and ever the empirical observer, dryly noted that “marital instability characterized many.”

Mr. Weil, the psychologist, brought his wife to the community and was among the few participants whose marriage survived. “I do remember a kind of loosening of sexual bounds,” he said. “It was like a love fest.”

Did the Zihuatanejo Project achieve its goals? Mr. Weil isn’t sure. “The intent, as I reflect now, was to form a more concentrated network, a more concentrated group who could carry on the work. How naïve we were in terms of our belief that we could change the world overnight!”

Humanity was certainly not remade. Nor did their experiment persuade the scientific community to carry on research. The United States soon outlawed hallucinogens.

Psychedelic drugs are having a moment

But seeds were planted. After years of legal and scientific exile, hallucinogenic therapy is having a resurgence. One can find ketamine clinics in major cities, and studies of the helpful effects of MDMA, better known as the party drug Ecstasy or Molly, on Post-Traumatic Stress Disorder have pushed the drugs closer to therapeutic approval. Young creatives and tech workers are also gravitating toward microdosing themselves with LSD or psilocybin mushrooms as a cure for depression or a creativity booster, although the science is still unclear.

For the last decade, an increasing number of tropical psychedelic retreats around the world have attracted travelers looking to change their minds through hallucinogenic drugs.

After the trippers were kicked out of Zihuatanejo, the town gained a certain popularity among celebrities unconnected to the Leary crowd. John Wayne liked to sail his boat down from California. The actress Lauren Hutton and later Keith Richards of the Rolling Stones vacationed there. A burst of tourism development starting in the 1980s increased the population from about 8,000 to what it is now, 126,000.

Long gone is a lifeguard tower with a room draped in Indian prints, into which one tripping member of the group rotated every 12 hours. It was called the “soul” of the IFIF community. Mr. Bergtold said his family has worked to preserve the atmosphere of an isolated tropical garden, even as villas light up the night on what used to be dark jungly mountains nearby. “Lots of people say your place has a magic,” he said. “When I wake up there, I feel like the soil is giving me life-growing energy.”

Mr. Weil, whose vitality he attributes to more than 50 years of tai chi, never lost touch with that other period of his life. After abstaining from psychedelics for decades, the pandemic lockdown provoked him to drop back in. In the past year he has occasionally taken a dose of psilocybin in his office in the mountains outside of Boulder, Colo. He said it helps him process aging and childhood trauma.

His reacquaintance with psychedelic drugs comes as a new generation of psychedelic therapy enthusiasts have been calling on him lately to share his wisdom. After 10 or 15 minutes, he said, “I don’t need a guide. It’s like riding a bike, it comes back.”

Nina Burleigh is a journalist and author, most recently, of Virus: Vaccinations, the CDC and the Hijacking of America’s Response to the Pandemic.

Follow New York Times Travel on Instagram, Twitter and Facebook. And sign up for our weekly Travel Dispatch newsletter to receive expert tips on traveling smarter and inspiration for your next vacation. Dreaming up a future getaway or just armchair traveling? Check out our 52 Places for a Changed World for 2022.