On a Friday evening last spring, Zack Woodruff picked up two college friends and drove seven hours down Interstate 65: through Indianapolis, bourbon country and the rolling hills of Appalachia.

In the middle of the night, they arrived at Miguel’s Pizza in Slade, Ky., and pitched tents in the backyard, near a gear shop that sells rock-climbing equipment. They were destined for the nearby Red River Gorge, a dramatic rocky cliff that Mr. Woodruff has explored eight or nine times.

But Mr. Woodruff, 28, a Ph.D. candidate in robotics at Northwestern University, lives in Chicago, so most of the time, he climbs at First Ascent, an indoor climbing gym with four locations in the city, where, he said, “a lot of grad students climb after work.”

Over the past five years, rock climbing has become a popular activity among young professionals and families, documented on social media and in films like “The Dawn Wall,” “Valley Uprising” and “Free Solo,” an Oscar winner that chronicled Alex Honnold’s ropeless ascent of El Capitan in Yosemite National Park.

In 2016, rock climbing was added to the 2020 Olympics. New climbing gyms are mushrooming like cycling studios before them, and U.S.A. Climbing, the competition circuit, signed a multiyear broadcast deal with ESPN in January.

Popular street wear brands have been mining “old-school climbing stuff” from North Face, Patagonia, Eddie Bauer and L.L. Bean for inspiration, according to Matthew Schonfeld, 27, a climber who lives in the Crown Heights neighborhood of Brooklyn and does marketing for Rowing Blazers.

“It’s a moment, you know?” said Jimmy Chin, 46, who directed “Free Solo” with his wife, Elizabeth Chai Vasarhelyi. “These moments happen when a bunch of different variables all line up.”

According to Climbing Business Journal, which tracks gym openings nationally, the commercial climbing gym industry grew at a rate of 6.9 percent in 2016, 10 percent in 2017 and 11.8 percent in 2018.

“It does seem like the growth of the gym industry is continuing to trend upward,” said John Burgman, 38, a journalist who writes Climbing Business Journal’s annual report and coaches a youth climbing team in Carmel, Ind.

Most rock gyms look equal parts Flintstone and Jetson; visiting one feels like landing on a Technicolor planet, or exploring a cave bedecked with Fruity Pebbles.

There are two types of indoor climbing walls: bouldering walls, which are low enough that climbers can leap (or tumble) onto the mats without getting hurt; and top-roping walls, which tower over the bouldering walls and require harnesses, ropes and a partner on the ground belaying the rope — or gathering the slack as you climb higher — so you won’t fall too far if you slip. The sport has its own arcane terminology, with difficulty ratings like V5.

Young professionals flock to these playgrounds after work because the exercise is intense, unstructured and sociable; the gyms may be one of the last urban locales where talking to strangers is encouraged.

Engineers in particular seem to be attracted to the sport, because each “boulder problem” of holds is a three-dimensional puzzle, and gyms reset them monthly to keep things spicy. (As part of its corporate wellness program, Google installed a rock wall in its New York offices in Chelsea, in 2013. Its Bay Area and Los Angeles offices have rock walls, too.)

And for parents, climbing is part of the so-called free-range-kids movement — with proper supervision, of course, the antithesis of the dreaded screens.

“If you walked in and saw my itty-bitty 5-year-old, you’d be like, Oh my gosh! She goes high. She goes to the top, and she’ll rappel,” said Megan Novotney, 36, a yoga teacher whose 6-year-old triplets also partake, sometimes rappelling down together while holding hands.

“When they’re bouldering, they don’t climb anything higher than what they know they’re capable of getting down from, and that was really awesome because it translated over to the park too” Ms. Novotney said. “I trust them, and they trust their bodies.”

Adults, of course, are also relishing the chance to unplug themselves, and those not partial to yoga’s chants and group movement may find a more individualist escape on the wall.

“It’s active, it’s good for you, you have to try hard, it makes you feel very present in the moment,” Mr. Chin said of yoga, “and I think climbing does a lot of those things. It’s one of those activities where you do actually need to put your phone down and you do actually have to be engaged, and for some reason it’s easy to have conversations and talk to people you don’t know when you’re climbing.”

“When you’re climbing,” he said, “there’s also a certain level of vulnerability, because you’re scared and you’re all having a shared experience, especially if you’re trying the same climb.”

Growing up in Mankato, Minn., he didn’t know climbing existed. When he started, 25 years ago, “climbing was a pretty fringe activity,” he said, “and it was usually kind of like the misfits, who couldn’t play ball sports, or weren’t great at team sports.”

These days, there is a climbing gym in nearly every major city. Corporations like Touchstone Climbing, El Cap, First Ascent and Brooklyn Boulders have plans to build more.

Sasha DiGiulian, 27, is a three-time United States National Champion climber who helped design a climber emoji and now hosts high-end climbing wellness retreats in Kalymnos, Greece.

There, groups of 16 to 20 — often millennials from Silicon Valley, San Francisco and New York City — shell out $3,500 for luxury accommodations, four days of climbing with Ms. DiGiulian and three guides, dinners of freshly caught fish and ouzo, and a rest day swimming with wild dolphins.

Her clients are “young professionals looking for an experience,” she said, and since it is tough to switch from gym climbing to outdoor climbing, she created the retreat to “facilitate people’s transition.”

Ms. DiGiulian believes that the climbing industry is expanding in tandem with boutique fitness, citing Brooklyn Boulders’ boutique fitness branch in Boston, BKBX, which combines rock climbing with high-intensity interval training (HIIT).

“They’re opening these boutique studios that are dedicated to optimizing your fitness in order to ‘train for your next adventure,’ is their slogan,” she said. “They’re not even the traditional sense of climbing, it’s climbing broken down into a fitness class. That definitely didn’t exist even five years ago.”

Harley Pasternak, who trains celebrities including Ariana Grande, Kim Kardashian West and Gwyneth Paltrow, isn’t a fan of rock climbing. None of his clients do it, though climbing makes a few appearances in Goop.com’s travel pages.

“It’s really not a full-body workout,” Mr. Pasternak said. “Most of the muscles that people really need to strength-train — hamstrings, glutes, lower back, rhomboids, triceps — are not really worked during rock climbing. Rock climbing is mainly lats, forearms, quads and calves, so these are not going to contribute to better posture.”

Not to mention, he said, most people aren’t strong enough to hoist themselves up a wall without getting hurt.

“Keeping in mind the average American is significantly overweight, I would talk everyone I could out of rock climbing unless you are incredibly light, agile, fit and functional,” said Mr. Pasternak, 45. “There is a very small minority of this country that should be rock climbing.”

He pointed out that the British Journal of Sports Medicine tracked a 36 percent increase in rock climbing injuries from 2006 to 2015, 12 percent of which required hospitalization. Young men were most frequently injured.

Mr. Pasternak also pointed out the absurdity of humans constructing elaborate sheltered courses to challenge themselves

“That’s connecting with nature the same way that spinning in a room is connecting with nature,” he said. “They’re both contrived, artificial versions of the real thing without any connection to nature or the outdoors.”

Indoor climbing gyms can be expensive, especially in cities like New York and San Francisco. “Unless the commercial real-estate landscape changes, you can’t offer membership for less than $90” per month, said Michael Cesari, 39, the owner of Steep Rock Bouldering in New York. “It’s a bummer because when you go elsewhere, it’s not the case with indoor climbing.”

In other parts of the country, climbing has become so accessible that there are places that allow climbers to volunteer at the gym if they can’t afford a membership, like Memphis Rox in Tennessee, or YMCAs that offer it for free.

At Brooklyn Boulders, near one of the slanted bouldering walls — the shorter walls without ropes — a diverse group of young people were sitting on the mats and catching up on a recent Saturday while two dogs frolicked in the waiting area.

“We barely climb,” said Aaron Stack, a 30-year-old software engineer. “No one here actually likes climbing, we all just come here to hang out. The climbing is ancillary.” (He was joking: They’ve all been climbing for years, and have a weekly brunch after their workout.)

Unexpectedly, Saturday mornings are pretty quiet at Brooklyn Boulders and other gyms. Peak hours are weeknights after work, and the really serious climbers go in the morning before work.

Waiting patiently and considering courses has long been part of the indoor-climbing culture, and yet. “There’s always certain times when it’s crowded, but those crowded times have gotten more crowded,” said Michael Poyatt, 25, a software engineer in San Diego who started climbing after seeing “The Dawn Wall.”

Dan Bartz, 36, a founder of First Ascent in Chicago, said his company is trying to avoid crowding issues by opening new locations and requiring new members to attend orientation classes.

“I think there is the risk that you can have the longtime, established climbers and the newer climbers and there can be a tension between those two groups because the experienced climbers know how to behave in a climbing gym,” Mr. Bartz said. “They know where to stand, and they know how to share resources like routes or boulder problems.”

The majority of new climbers follow the rules, but some don’t. Mr. Stack witnessed an incident firsthand.

“One time, I saw these two people climbing, and it was their first time climbing, and it was on the overhung wall, and the one person fell and swung and knocked over the person belaying,” he said. “The one belaying stopped, took both of her hands off the rope, picked up her camera, and took a picture of her friend. There’s just been a huge influx of people with no clue what they’re doing.”

As a result, gyms have had to add extra safety programming; nearly all require climbers to sign a waiver and take a class before they can climb on their own.

In order to compete with the Equinoxes of the world, many climbing gyms offer weight rooms, cardio machines, yoga classes and Wi-Fi. Some are now also installing cafes and co-working spaces.

“Starbucks always talks about being people’s third place, and that’s really our goal too,” Mr. Bartz said. “People have home and they have work and we want to be that third place they go to and spend time connecting with people.”

Mr. Cesari likened the sport to snowboarding, whose addition to the Olympics, he pointed out, did not cause a lasting surge in popularity.

“For how many people will climbing be a lifelong sport, which they will then pass down to their kids? That’s the big question,” he said. “Of course people are going to change gyms, they’re going to move, but are they going to join another one? Or is it something that’s more of a temporary hobby?”

There is also a stereotype of the “boulder bro,” perhaps intermittently fasting to improve his agility, showing off his calluses, rocksplaining.

“If you want to climb really hard, you have to take your shirt off, and you have to wear a beanie,” Mr. Stack joked. “You also need a really big chalk bag, like twice this size, you leave it on the ground below you, preferably under where you’re climbing, so when you fall on it, it goes ‘poof!’ for dramatic effect.”

But in fact climbing is more diverse than ever. Brooke Raboutou, 18, made headlines earlier this year when she became the first American to qualify for the Olympics. “I would say that the climbing ratio of men to women is still about 60 percent to 40 percent,” Ms. DiGiulian said. “There are far more professional male climbers then there are professional female climbers, and I think the way climbing is changing, you are seeing a lot of people from different backgrounds getting into the sport and excelling.”

Though the sport is still overwhelmingly white, organizations like Brown Girls Climb, Melanin Base Camp, Brothers of Climbing and Color the Crag help climbers of color connect with one another.

Anna Marie Jennings, 23, met her closest friends in New York through Climb Like a Girl classes at Brooklyn Boulders. “Finding a group of women to climb with was really great because the gym is intimidating as it is, whether there’s all men around or all women around or whatever, just the nature of it can be overwhelming if you’re new,” she said. “It is very physical and people watch you, so that’s intimidating no matter who you’re around.”

“There are still times where I walk in and you’ll see, for lack of a better term, the bro-y guys muscle their way up a really hard boulder problem, and I may not be able to do it from strength,” she said. “But I might have more flexibility or balance.”

Ms. DiGiulian has been a pioneer for women in the sport, and grew up climbing the Red River Gorge, where Mr. Woodruff and his friends camped in Kentucky. A high point of her career was achieving a climb there called Pure Imagination, one of the hardest to be finished by a woman.

This “used to be one of the poorest districts within Kentucky, and now it’s blooming with business,” she said. “When I started going to Miguel’s, it used to be a little ice cream stand. Now I’ll be in countries like France and Spain and see someone wearing a Miguel’s Pizza Shop T-shirt.”

Dario Ventura, 35, the co-owner and manager of Miguel’s, said that since his father Miguel went into business 35 years ago, foot traffic has grown “exponentially.”

To adapt, Miguel’s Pizza renovated its kitchen and country-store restaurant, tripled the size of its campsite, and now employs a staff of 42 mostly transient climbers, many of whom live out of vans, like Alex Honnold in “Free Solo.”

The local community in Slade has also adapted. Nowadays, Mr. Ventura said, there are three search-and-rescue teams that respond to calls in the Red River Gorge, where previously, there weren’t any. “The whole area has grown too, there’s a ton of restaurants now, there’s a ton of campsites to compete, and we’re all full every weekend,” he said. “It’s a really healthy environment.”

However, the gorge has been subject to littering and crag erosion from the crowds. There have been efforts by the Access Fund, a nonprofit climbing organization, to maintain the bolts in the rocks so they don’t wear down from overuse and pop out dangerously while climbers are on the rocks.

Mr. Ventura marveled at all this activity. “For so many years, you got into rock climbing because you had some crazy uncle that took you out, but with climbing gyms being so accessible and everywhere now, there’s this giant funnel of people that are getting into climbing in urban areas and come here on the weekends,” he said.

And yet “I’ve heard some numbers where something like 10 percent of all people that climb in a climbing gym actually go climbing outside. Which is mind-boggling to me.”