In Azerbaijan, site of the COP29 climate talks and a petrostate, people aren’t only proud of their oil. They swear by its health benefits and visit resorts to soak in it.

I bathed in oil during the U.N. climate summit.

It was crude oil from a half-mile underground, pumped into a bathtub at a hotel in Azerbaijan. It crept into every crevice of my submerged body and every fold of my skin. It smothered the hair on my limbs, making me look a little like an animal stuck in an oil spill.

Then came an attendant to scrape it all off.

Just a day earlier, I had been covering the United Nations’ annual climate conference, COP29, which is being held this month in Baku, Azerbaijan, a place that helped give rise to the modern oil industry more than a century ago, enabling and endangering our civilization.

Much has been made of the incongruity of those fighting to reduce fossil-fuel emissions gathering in a petrostate, but Azerbaijanis are proud of their oil, whatever conference attendees might think of it. For instance, it fueled the Soviet defeat of the Nazis in World War II.

Another point of pride lies beneath the dusty, shrub-dotted hills of Naftalan, a city a four-hour drive from Baku. The chocolate-colored oil extracted there doesn’t burn. Instead, the locals and Azerbaijani scientists say, it heals. If you bathe in it.

But this oil, like all oil, is a finite resource. Naftalan’s recoverable deposits of “medical” oil were already halfway gone as of 2022. So the photographer Emile Ducke and I traveled there for an intimate encounter with the dwindling substance.

“They tell us that we’ve got reserves for 60 years,” said Ayten Magerramova, the head doctor at a Naftalan resort called Garabag. “After that, I don’t know.”

Once you bathe in crude oil, it’s hard to get rid of it. For that reason, the Garabag’s towels, bathrobes and bedsheets are all brown. My bed’s headboard had light brown stains. In the brown bathtubs in the spa area, the resin left over after draining the crude was almost black.

“The resin itself is a bit toxic,” Dr. Magerramova said. “But for skin problems, the resin really helps.”

Petroleum’s use as medicine goes back millenniums. Marco Polo, who traveled through present-day Azerbaijan, described its oil as a “salve for men and camels affected with itch or scab.” The Soviets said the unusual molecular makeup of some of the hydrocarbons in Naftalan’s oil made it suitable for treating arthritis, infertility, eczema and a host of other medical conditions.

There’s little Western research on the risks and efficacy of the oil, but an article published in 2020 in an Azerbaijani science journal reported that the oil has been found to work as an antiseptic and to have a “peculiar hormone-like effect on the function of sex hormones.”

Aydin Mustafayev, 62, a Naftalan native, remembers people digging wells by hand when he was a child. They filled their own jars with the oil and brought it home to treat the wounds of turkeys, dogs and sheep.

In 1995, Mr. Mustafayev returned from fighting in Azerbaijan’s war with Armenia. He recovered from his back injury, he said, by bathing in Naftalan oil for three years. Now, he oversees Naftalan’s 32 wells for SOCAR, Azerbaijan’s state-run energy company.

SOCAR gas stations are ubiquitous on Azerbaijani roads. In Naftalan, the company also delivers the local healing oil in its tanker trucks to about 15 resorts, which last week were attracting Baku residents escaping the crush of the climate conference.

Rita Dadasheva, 64, a schoolteacher, had previously sought out Naftalan oil treatments in Baku for her arthritis. But you could tell by the color, she said, that the oil was fresher closer to the source.

“The Naftalan here is the color of melted milk chocolate,” she said. “It’s just what you need.”

At another resort, Nafta, the head doctor, Zaur Valimatov, said he hoped to preserve the subterranean deposits for future generations by phasing out oil baths, which use copious quantities, in favor of oil wraps, which would use more modest amounts. In addition, he said, such wraps could reduce the toxic effects of crude oil’s “undesirable” components.

“Putting people in oil,” he said, “is a bit of a barbarian use of oil.”

Naftalan has seen a surge in visitors since 2020, when Azerbaijan recaptured part of the nearby territory of Nagorno-Karabakh, pushing back the line of contact with Armenian forces and making the city safer to visit. A woman from Omsk, Russia, said that more Russians started coming here “after the sanctions” — a reference to the fallout from Russia’s invasion of Ukraine.

The sanitariums reuse their oil for a few months before getting a new delivery, though they say they filter it after each bather.

Whatever the hygienic concerns, many guests — everyone I met came from a country that, like Azerbaijan, was formerly part of the Soviet Union — swore by the baths. Damira Vaitsel, 30, an executive assistant from Kazakhstan, said she’d successfully treated her psoriasis after two weeks in Naftalan. Bathing in oil, she said, made her feel like “the best oligarch in the city.”

Eventually, I decided I had to try it, too.

As the oil glugged toward my chest, I grew nervous, remembering what the doctors had said about its toxicity. Finally, the attendant turned off the flow and left me to ruminate on being enveloped in a viscous stew consisting of the remains of primordial creatures.

It was warm and pleasingly heavy, so the nervousness gave way to relaxation. It smelled something like paint, rubber or sour milk, but I grew used to it. I felt cocooned by this raw substance that helps define our lives.

I lifted my arms and legs and watched the rivulets. The oil matted down every hair on my arms and filled every cuticle, every line of my palms.

And then the weirdness of this substance hit me. Though it looked like molten chocolate, it wasn’t sticky — it was slippery. My foot slid across my shin, my hands slid over my hips. It was otherworldly — netherworldly?

When it was time to get out, exactly 10 minutes later, the attendant had me stand and grip a handle attached to the wall. Here I was, I thought, a chocolate-covered strawberry before the chocolate had hardened. The attendant scraped the oil off with a long shoehorn, methodically, from top to bottom.

He rubbed me all over with many oversize paper towels that formed a brown pile at my feet. He continued in the shower, using copious gobs of soap, before finally handing me a washcloth and directing me in broken and bawdy Russian to clean my more intimate parts myself.

Back in Baku, I sought to process the experience. At the climate conference, it was becoming clear we humans are failing to stop the planet’s warming to ever more dangerous levels.

So I decided to seek out the place where, in one sense, it all began: a site marked as the world’s first industrially drilled oil well, dating to 1846, now located in a Baku swimming pool parking lot. Nearby, between the Caspian Sea and newly built apartment towers, scores of green-and-red oil derricks still whoosh, creak, rumble and bang.

I stood watching the hypnotic bob of one of them as a worker, Khalid, 54, stood next to me in silence.

“Take it out, sell it,” he eventually said. “It’s like God sent this to us.”