When Kelly Hughes looks back on her teenage years, she remembers her basement.

There was plush, khaki-colored carpeting, an L-shaped couch, and a Wii game console that hooked up to a flat-screen TV, said Hughes, now 28. Monopoly, Clue, and a couple of puzzles were stashed in the closet.

As Hughes and her friends started junior high, that basement became the cool place to hang out: where they would gather, first to whisper about the boys they wanted to kiss — then, a few years later, to sit shoulder-to-shoulder with those boys, passing around a bottle of cheap liquor that someone had smuggled in under their clothes.

“My parents mostly left us alone in the basement,” Hughes said. “And even if they knew we were drinking, it somehow felt a little more secretive . . . More free.”

For decades, the basement has been the place where American teenagers go to grow up. At the bottom of the family home, separated from parents by a staircase and several layers of foam insulation, teens can test out things they’ve been told they aren’t quite old enough to try: R-rated movies, coed parties, alcohol, sex. In “That ’70s Show,” it’s where teenage friends retreat to smoke weed. In the movie “13 Going on 30,” it’s where 13-year-old Jenna Rink waits for her Seven Minutes in Heaven — and where she, quite literally, becomes an adult.

The basement doesn’t have the same significance in other countries, where families are far less likely to see it as a place for leisure. Instead, it’s used for storage or nothing at all, said Sarah Lichtman, a professor of design history at the Parsons School of Design. “The finished basement is a really distinctive American space, with definite connections to teens and coming of age,” she said.

Up until the mid-20th century, American basements or “cellars” were traditionally used to store crops: potatoes, onions and other root vegetables, hearty enough to last several months in a cool, damp space, said Thomas Hubka, an architectural historian who specializes in the American home. The basement-as-rec-room-tradition seems to have emerged in the postwar period, said Lichtman. In the 1950s and early ’60s, as American teens started to experiment with rebellion — listening to Elvis, protesting the Vietnam War, dabbling in hippie culture — parents were eager to keep them close. Magazines such as House and Garden and House Beautiful started featuring photos of finished basements and the happy teens who spent time there.

“These ads would show teenagers dancing or playing shuffleboard in basements,” sending a clear message, said Lichtman: “Keep teens at home. You don’t want them to go out and become juvenile delinquents.”

Around the same time, more and more American homes were adopting the technologies necessary for creating basements that were not, in Lichtman’s words, “really damp and gross.” Families installed air conditioners and dehumidifiers, and framed out a habitable segment of the space with sheets of drywall.

While many families such as Hughes’ have transformed their basements into luxury hangout spaces, a basement doesn’t have to be fancy to hold teen appeal. Maria Inocencio, a 59-year-old Filipina immigrant who grew up in a poor neighborhood in Long Island, remembers spending many long, happy hours in a friend’s dark, dingy basement that “kind of smelled.” Her friend’s older brothers had installed a black light, and covered the floor and walls with dozens of one-by-one-foot carpet samples. Inocencio and her friends would go there to dance to the Osmond Brothers.

“The other spaces in my life were all very exposed,” said Inocencio, who would sometimes get caught kissing her boyfriend on the porch outside her house. “My family had six kids, the neighbors had six kids, so someone was always watching.”

With the inherent privacy of the basement comes a different set of rules, said Lichtman. Guests you want to impress don’t usually go down there, so keeping it clean isn’t really a concern. It’s more okay to put your feet up on the table or eat in front of the TV or turn the music up loud or cuddle with a crush than it would be in the living room or the kitchen. “If you had a boyfriend in high school, the basement was where you went,” said Hughes. Multiple people said it’s where they lost their virginity. (The relative privacy of the basement also makes it a place where things might go wrong. There is a reason, Lichtman said, why the basement is a common setting for a horror movie.)

While basements are common throughout much of rural and suburban United States, there are certain parts of the country that don’t have them. In Phoenix, for example, the ground is too hard. In Florida, there is too much moisture in the soil. Across much of Texas, there are only a few inches of dirt before you hit limestone.

Where there are no basements, adolescence changes. It’s harder for teenagers to find a sense of autonomy at home, Lichtman said, and try new things in a place where they often feel at least somewhat protected. Without basements, teenagers looking for privacy spend more time in malls, parks, cars and diners, according to several basement-deprived young adults. (Garages, one Phoenix-raised millennial said, are another good option.)

“I guess you probably have more kids making out like crazy on park benches,” said Lichtman.

Now that Hughes and her three younger siblings have moved away, their family basement has reverted to its original function, from before its 20-year-stint as the ultimate teenage hangout: a home for things not in use.

There’s a bag of Hughes’ old sweatshirts from college, a bucket of arts and crafts supplies, a kids’ plastic walk-in kitchen, a few board games no one ever really played.

When she visits home now, Hughes hardly ever goes down there. There’s no real reason to, she said. She mostly hangs out in the living room, sipping wine with the other adults.

‘It feels like I’m sprinting towards a nonexistent finish line’: This is how I experience anxiety

‘I’m still trying to figure out how to best play the cards I’ve been dealt — that’s really all I can do’

Meet the 17-year-old climate activist who skipped school to hunger strike at the Capitol

Sophia Kianni was by far the youngest, and one of the only women, at the protest in Nancy Pelosi’s office

Millions of young people around the world strike for action to stem climate change

The strikes come three days before world leaders are set to gather at the United Nations on Monday for a much-anticipated climate summit