There's an unmarked black door at the end of a Pompano Beach strip mall, next to a laundromat and a dollar store and across the street from an Episcopal church. The only hint of what happens beyond the door is a worn sign leaning against a pole near the parking lot. It reads "Club Hedo."

Just after 11 p.m. on a recent Saturday, a young couple — a broad-shouldered man in slacks and a petite blond in her mid-20s wearing a polka-dot dress — walks through the black door and into Club Hedonism. It's their first time here, and a few people stare as they amble past the pool table, wide-eyed and a bit nervous.

The clandestine club would fit right into a pleasant snapshot from 1978. There's a disco ball, a wooden bar adorned with Christmas lights, vinyl chairs situated around a few Formica tables, and a parquet dance floor replete with a single metal pole. The young couple sits down on a leather couch. A mix of recent pop songs and older disco plays to the 20 or so people — nearly all between 40 and 60 years old — scattered about the room.

Soon enough, though, they're invited to join a group of regulars — two men and three women — seated at a table. Susan, a tall, 49-year-old blond in a chiffon dress, locks eyes with the young lady in polka dots, takes her gently by the forearm, and guides her to the chair next to her own.

Like most of the people contacted for this article, Susan asked that her last name not be published for fear that tales of her exploits might make it back to neighbors and coworkers. By day, she's a Broward public school teacher, but on weekends, she puts on a little extra makeup, wears a slightly shorter dress, and comes to clubs like this.

"Are you new to the lifestyle?" Susan asks the couple.

"This is our first time here," the young blond woman says. "We went to another club once, but we didn't do anything."

Susan asks if they want anything to drink. "I have every kind of liquor here," she says. "What do you want?" She fetches two rum and Cokes and a tall, strong pink drink for herself.

The Kinsey Institute at Indiana University estimates that as many as 4 million Americans participate in some form of group sex or couple swapping. With its welcoming beaches, year-round sunshine, and fine appreciation for vices, South Florida has become the mecca of swinging in this country. Couples make sexual pilgrimages here from points all over the world. At least four different swinger cruises depart from South Florida every year. While swingers anywhere can connect through websites and classified ads, South Florida has five on-premises sex clubs (four in Broward, one in Miami-Dade, none in Palm Beach) catering to a variety of different lifestyles.

The owner of Club Hedonism is a large Italian man in his 60s named Franco Monte. He can be found striding through his club with purpose, wearing black slacks, a black shirt, and a thick gold chain. His employees are diligent, because they know he's a perfectionist and they dare not upset him. Every inch of the club must be spotless. Every employee must embody a delicate blend of attentiveness and discretion. He says he wants people to think of his place as "the swingers' club where everybody knows your name." Like Cheers — but where the characters have sex with one another.

And yet, Monte says, "It's about much more than the sex. People can have a few drinks and dance a little bit and get to know each other." Key to the experience, Monte says, is the anticipation of having sex. "A pleasure of the mind," he calls it.

Here's how it works at Hedonism — and the concept is similar at the other clubs:

It's a private, members-only establishment, thereby not subject to public indecency laws or liquor laws. Prices range for individuals and tourists, but local couples pay $100 for a year membership, plus an additional fee per visit ($50 on Fridays).

The club is divided into two parts. The front room serves as a nightclub. Guests bring their own alcohol, but mixers are provided, and bartenders make the drinks. There's a small buffet (complimentary with the price of admission) and a dance floor in front of a wall of mirrors.

Then there's a back section. Once visitors get comfortable, they generally move into this area, which is partitioned off into a maze of separate lounges. The "love parlor" has turquoise walls, a red pleather couch and chair, paintings that would not look out of place at your grandmother's house, and porn broadcast on a small TV mounted on the wall.

A massage room and "group playrooms" have industrial carpeting, more vinyl-covered tables and cushions, and sex toys. Walls painted back, white, and purple add a gothic feel to some of the rooms. A "fantasy suite" includes six queen-sized mattresses. These rooms are where the orgies take place.

Unlike the other clubs in South Florida, which require guests to remove their clothing before going into "play areas," at Hedonism, you can undress — or not — whenever or wherever you like. Early in the night, the back area is quiet and empty. But by midnight, people have limbered up, and the hallways echo with a cacophony of guttural moans.

Monte opened Club Hedonism in 1974, but he tells people that partner-swapping dates back to the days of Julius Caesar. "Everything began with Romans," he says, "the public orgies."

The first accounts of swinging in America came from military couples near the end of World War II. By the 1950s, the phenomenon had spread to the suburbs. But the modern, mass-market form of swinging didn't come about until the early 1970s, on the heels of the sexual revolution. That's when Plato's Retreat, America's first on-premises swingers' club, opened in New York, in the cavernous basement of the Ansonia Hotel, in a defunct gay bathhouse where Bette Midler and Barry Manilow performed early in their careers.

Almost immediately, similar clubs started opening in Boston, in Chicago, in Los Angeles. Deenie's Hideaway opened in Coconut Creek in 1973, and a handful of other South Florida clubs followed suit.

Monte has seen the evolution firsthand. "In the '70s, swinging became a big trend," he says. More private, so-called "bi-wives clubs" popped up in neighborhoods across the country. By the end of the '80s, a new fear of sexually transmitted diseases — most notably HIV/AIDS — gave America pause. "That scared a lot of people away," he says. Many of the biggest clubs, including Plato's in New York, closed. In the '90s, a series of raids on South Florida sex clubs scared even more people away, even though the criminal charges were dismissed.

So for years, Monte says he kept his club out of any kind of spotlight. He has the small sign that stands out front, but he puts it up only on weekend nights. His business subsisted on word-of-mouth advertising. "One couple would come here and have a good time, then tell a few of their friends. Then they'd tell a few of their friends."

The majority of people in this subculture are middle-class couples who live conservatively in other aspects of their lives. In researching his book The Lifestyle, published in 1999, journalist Terry Gould found that a third of the group-sex participants he spoke to had postgraduate degrees, almost a third voted Republican, and 40 percent considered themselves practicing Protestants, Catholics, or Jews.

Says Monte, as he prepares for a busy weekend night that will include dozens of couples: "This is as liberal and open as it's ever been."

Mark and Karen, a couple in their 50s, have been coming here for more than ten years. His slicked-back dark hair matches his closely cropped beard, and his white, buttoned-down shirt is undone to his sternum, revealing a large dragon medallion. Karen, a short, shapely blond, has on a sheer, white Guinevere-style dress with a slit up the side and carries a silver lighter with the word Slave engraved across it.

"The way I look at it, monogamy is a carryover from the feudal system," Mark says. "Men went away to war and didn't want to have to come back and raise some other guy's kid. But we live in a time of birth control." Jealousy, he says, is just thinly veiled insecurity. As he speaks, he caresses Karen's leg. "We don't need to try to control each other."

Susan is on her third drink, and she's still flirting with the young blond. She explains that she came of age in the '70s and always had a bit of a wild streak. She got into "the lifestyle" — the most common term used to describe swinger culture — six years ago with her husband. They started "soft swapping" — when the women engage each other but there is no interpartner intercourse.

In the beginning, they would swing only with single women. After a few years, though, there was a guy or two she "felt like going all the way with," and they began "full swapping." Although she was afraid she would get jealous, she said that when they finally crossed that line, "I just didn't feel territorial... It was titillating to watch."

Because of her work as a teacher, she was always terrified that someone might see her. But that was also part of the thrill.

Susan steps outside for a moment to smoke a joint with her friends, then returns, still reminiscing about her husband. "An incredible man," she says. This used to be their favorite club. But one night three months ago, he suddenly died. They'd gone to the club that night. When they got home, they finished off a passionate evening in the bedroom.

"You know how every woman gets up and walks to the bathroom after sex?" she says. "Well, I had just gotten up, and when I came back, he was on the floor."

She recalls moments they shared here, some charming, some erotic, and some gross — like the time he dropped his ring and ended up digging it out of a trash bag full of used condoms.

Unlikely as it may seem, Susan says, fellow swingers have become some of her closest friends. Mark and Karen call her at home to see how she's doing. They get her out of the house. As Mark hears Susan telling her story, he slides his hand over her leg. "We look after one another here," he says.

One of Susan's friends, Sandy, dances around the table in a short, white, tennis-style skirt and a vest with nothing underneath. "When everything gets going, it's like there's some kind of pixie dust in the air," Sandy says. "Sex is contagious."

Sandy, who never reveals her age but looks to be in her mid-50s, has been swinging for nearly 40 years and says she still loves it. "It's one of the only places you can get naked in public, for starters," she says. Then she removes her vest.

Tonight she's here with Luis, a rather large, bearded biker she's been dating for a few weeks. They met at a motorcycle rally, and Sandy invited him to the club. He doesn't drink or do drugs — he counsels teenaged addicts, as a matter of fact — and he doesn't mix the biker club with the sex club.

As the night rolls on, Luis asks someone for a pen and jots a note on a napkin. He slips it over to Sandy. The note reads: "Would you like to be my girlfriend? Circle one: yes no maybe."

Sandy lets out a drunken snicker. Then she folds the napkin and gently tears it in half.

Each of the five swingers' clubs in South Florida is geared toward a slightly different demographic and has its own rules and unique characteristics: Miami Velvet, the only swingers' club in Miami-Dade, caters to a young, South Beach crowd. The décor is modern: red and purple walls, velvet couches, and a few cages. Membership costs $200 a year for local couples, and there is a strict dress code.

The Rooftop Resort in Hollywood is a hotel that's especially popular among Europeans. On rare occasions, there is some tension between its mixed clientele of traditional nudists — who often downplay the connection between nudity and sexuality — and swingers, who might have a threesome where the quiet sunbathers normally sit.

Tucked into a wooded stretch of Hillsboro Boulevard in northwest Broward is Deenie's Hideaway, the longest-running on-premises swingers' club in the country. The building is set up like a large house, with social areas downstairs and bedrooms upstairs. The décor is bright and colorful, à la Martha Stewart. It's not rare to find someone napping on a bed or unopened condoms in the parking lot. (Susan, who prefers Hedonism, calls Deenie's the "truck-stop swingers' club.")

The busiest time at Deenie's is Sunday afternoons, when about 20 couples — and a few single men and even fewer single women — come out to party. Everyone here is in the late-30s-to-early-60s age range. There are toned, tanned business types and plump, relaxed retiree types. They are white, black, Hispanic, and Asian. Today, there are couples playing volleyball in the pool, a few more drinking in the hot tub, and a few men hovering around a supersized grill. Three women talk quietly at the bar. About half the people here are wearing clothes. If you didn't know that a few couples had wandered upstairs — where no clothes are allowed — to have sex with one another, it might seem like a backyard barbecue with a few nudists.

On a recent Sunday, two women in their late 40s, both wearing bikini tops over their surgically enhanced chests, are making out on a deck chair next to the swimming pool. Their respective husbands, each holding a beer, stand about ten feet away, their eyes fixed on the women. Neither man says a word. There are a few colorful tropical drinks painted on a wooden wall behind them beneath the text: "It's 5:00 O'Clock Somewhere."

Anthony, a barrel-chested bald man with tattoos who's wearing a tank top, shorts, and flip-flops, says he's been in the lifestyle since he was 16, when a family friend finagled him into Plato's in New York 30-some years ago. "People come to Deenie's from all over the world," he says. "We just had one couple in here from the Netherlands and another one from Colombia."

Most swingers agree that the men usually suggest visiting the swingers' club but that the women decide whom to swap with and have veto power. A horny man would screw anyone, so the logic goes. But a woman is a more sophisticated creature, more discerning when selecting partners. First moves begin with eye contact. "If you see her looking at you more than once, she's at least curious," says Stephanie, a Deenie's regular. From there, women might make small talk, have a drink or two, dance, and introduce each other to their husbands. Regulars have the entire hookup process down to an inelegant science.

"It's basically like any other kind of club where people are trying to pick each other up," Stephanie says. "But it's with sets of two instead of singles, and if everyone is feeling a good vibe, you eventually make your way upstairs."

At Deenie's, a one-year couples membership costs $150, and there's a door charge of $35 to $50 depending on the day. A handful of regulars has "charter memberships," meaning they pay an annual fee of $5,000 and have total access to the club any day of the year. But, Anthony points out, even these members are subject to club rules, specifically the rules regarding touching others. "No means no here, and we're very protective," he says, his Big Apple brogue on full display. "You get asked to stop more than once, you get asked to leave."

Anthony says that swinging has grown exponentially with the evolution of the internet. Swinging has always been about connecting with like-minded strangers, and there's no place better for that than online. "It's like swinging on steroids," Anthony says. Swinger-centered dating sites like sdc.com (Swinger Dating Service) and lovevoodoo.com boast millions of swinger profiles — tens of thousands in South Florida alone. Couples and singles post photos — some risqué, some not — and sexual preferences. The sites then collaborate with clubs to host large parties where long-lusting swingers can finally meet face to face.

"It speeds up the whole process," Anthony says. "It makes it easier to find the people who like exactly whatever freaky thing you like and thought nobody else out there could possibly like. There's someone else out there."

Anthony says that recently more than ever, he's been getting couples as young as 21 at the door of Deenie's. "I tell them to go home and think about it first," he says. "If you're 21, we'll let you in, but swinging that young can be, well — " he pauses, parsing his words carefully. "Swinging can make a good relationship even better, and it can make a bad relationship even worse."

Nearby, a couple is smiling and laughing with a heavyset, dark-haired woman, the three of them all holding hands. After a day of fun, the couple heads for the door, and the woman goes back to the hot tub.

"That's Della," Anthony says. "She's one of the few single women who come here." He explains that in the swinging community, single bisexual women are rare. So rare, in fact, "they're called unicorns," he says with a grin. Single men, by contrast, are sometimes called "vultures." There are entire glossaries dedicated to swinger terminology.

Anthony explains that the woman who runs the place, Marja, is the wife of the original owner. He still drops by sometimes, but she oversees the day-to-day operations. Tonight, Marja is at the bar, having an intense — at times flirtatious — conversation with a man in his early 30s. It's been going on for hours, and she's made it clear she doesn't want to be distracted.

"Our customers are our first priority," Anthony says. "And she's customer number one."

If Deenie's is like your neighbor's house and Hedonism is like your neighborhood bar, then Trapeze is the megaclub where anonymity is part of the draw and group sex has a strong, animalistic quality, like something Caligula might have attended. "A free-for-all fuck fest," as a bartender so eloquently described it.

Trapeze is the biggest and best-known swingers' club in the country, with 10,000 registered members. The club's location on a busy stretch of State Road 7 means thousands of people pass it every day. There's a big, bright sign on the building and an expansive parking lot full of European sports cars parked by the valet. The inside features understated, sophisticated modern décor, with white booths, white walls, three bars, a massive buffet spread, and sparkling chandeliers. Literally hundreds of couples visit this 9,000-square-foot space on any given weekend, each paying around $75 at the door on top of a membership fee of $50 every three months. "It's a pretty economical date night," one regular says, "especially considering you're guaranteed to get laid."

During a recent costume party, the club is filled to capacity. The air sparkles with glitter. Pop songs thump through an expensive speaker system, and corresponding videos play on flat screens over the dance floor. Other screens show porn.

One woman is dressed as a "bedbug," with antennae on her head and a small bed hanging around her neck. A couple has painted blue every inch of their bodies — every inch — for their Avatar costumes. A man has a cardboard box advertising "free mammograms." Another man is dressed as Bill Clinton, an outfit that includes a portable lectern with the legs of a Monica Lewinsky sex doll hanging out of the bottom. (One of the managers, a man known as "Little Allen," tells the judges in the costume contest not to pick Bill Clinton because "he's a ringer" — he wears the same costume every year.)

Holiday parties are big here. For Halloween, the club had five different parties, with names like "Ghouls Gone Wild." For Thanksgiving, there was "Pornucopia." (Members entered raffles to win bundles of adult movies.)

As the night goes on, a tall, slim woman dressed as a fairy approaches another woman dressed as an angel, whispers something in the woman's ear, pulls down the top of the woman's dress, and begins gently biting her nipples. Nearby, a bald man in a zoot suit receives oral sex from a woman in a cheerleader outfit. More than one guy sports a Hugh Hefner costume.

All the food — a delectable spread that includes pecan-crusted salmon, spinach-stuffed chicken, a carving station and a salad bar, and a small fountain of chocolate for dessert — is cooked in-house by a team headed by a Haitian man named Maurice. Around 1 a.m., the luscious dinner buffet turns into a large breakfast buffet. The carving station becomes a gourmet omelet bar. There is a strict no-nudity policy around the food.

"We want to do everything within our power to enhance the entire evening," Maurice says. He's worked at the club for 12 years, and although club rules forbid employees from participating with patrons, couples sometimes invite Maurice to the back. He always declines, though. "I like my job too much."

The "playrooms" are set off by frosted double doors with a bouncer standing guard. But before anyone can go through them, all clothes must come off. Members are directed into a locker room, where they are assigned a locker and offered a crisp, plush towel. Ladies must remove their high heels; they can damage the furniture.

The backroom is divided into two parts — a couples side and a singles side — with a bar in between, manned by a chipper bartender in a red corset who lines up plastic cups of ice water for overheated participants. Each side has a bay of four vinyl-covered mattresses pushed together and a row of private rooms and curtained alcoves. There are also couches and sex swings throughout the place. The ceiling is mirrored.

By midnight, hundreds of people are scattered about the backroom, an orgiastic mass of flesh and overlapping bodies. The same music pumping over the dance floor plays in here. In the darkness, faces seem to blur, and names, ages, and occupations all fall away. Bowls of condoms are placed around the rooms. Plenty of people are using them, and plenty of people are not.

At one point, Cee-Lo Green's song "Fuck You" comes on. "I see you driving 'round town with the girl I love, and I'm like, Fuck you!" There are bare asses in every direction. On a mass of beds, six men and eight women are divided into three groups, with members rotating. One man thrusts into a woman from behind as she performs oral sex on another man who is kissing another woman as that woman is straddling a man who looks like he's either in immense pain or staving off an orgasm — or both. "I guess the change in my pocket wasn't enough, I'm like, Fuck you! And fuck her too!" The couches around the bed are filled with naked bodies, most paired off with either the woman on top or bent over, facing the wall. A few couples just hold hands and caress each other as they watch the bedlam. A man and a woman both fondle the breasts of a young blond who is watching a couple vigorously making use of a sex swing. "Although there's pain in my chest, I still wish you the best with a... Fuck you! Oo, oo, ooo."

Around 1 a.m. in the Trapeze locker room, people are in various states of undress, with some ready to play and others all played-out. The giggles and flirtations are drowned out when a woman starts shrieking. A lean brunet in her 20s and her boyfriend, a tall, muscular blond with a square jaw, are both naked, fighting next to their lockers. She's slapping him about the face and neck with both of her hands and screaming.

"She was on you," the woman yells. Her tears smear the glitter on her cheeks. "I saw it."

"No," he says, trying to shield his face from his girlfriend's nails. "She wanted to. It was close, but — "

"You're fucking lying! How could you?! How could you do that?"

She kicks him in the shins. A six-foot-five, 250-pound security guard tries to get between the two of them, but he's also trying not to touch either naked participant more than he has to. A crowd of dozens has gathered around. Blood drips from the boyfriend's nose. Finally she leaves the locker room, still crying.

"What's going on?" a man whispers.

"Her man fucked another woman without a condom," a woman standing nearby says.

"He totally deserves it then," says another woman.

"Eh," shrugs the whispering man. "Things happen."

When things finally wind down at Trapeze, hours of decadence are visible on the floor of the backroom. There are ice cubes and spilled drinks, moist latex and a plethora of bodily fluids. A few couples are still going at it as the cleanup crew — mostly Haitians wearing T-shirts and rubber gloves — begins to pick up the condoms and wipe down the vinyl. When everyone's out, the crew will bring in the wet/dry vacuum. They'll wipe down every surface, wash every sheet, and spray deodorizer. Soon the place will be ready for another night of sybaritic splendor.

Over at Deenie's, the place has quieted by sundown. In the lounge just inside the front door, a man in jean shorts and a T-shirt smokes a cigarette as he sits between two televisions. One TV is playing a porno; the other is playing an old episode of Cops. He's watching Cops.

When things wrap up at Hedonism, Sandy puts her vest back on and announces she and Luis are going home — probably to have sex. She gathers the pieces of the napkin she'd torn earlier and puts them in her purse. She has her arm around her partner, but she turns and flashes her chest to the group before walking out the door.

Susan downs the last of her pink drink and moves ever closer to the young blond. She knows this lifestyle isn't for everyone. Some people will never be able to separate love and sex. They'll never understand why anyone would want to share a partner or bring a private moment into the public. They won't crave that feeling of letting go, of indulging. Some people can't take the overstimulation or the way swinging can change the way participants think about their fellow human beings.

But for people like Susan, it feels right.

She puts her hand on the younger blond's leg and leans in close as she talks. "You're so beautiful," she tells the young woman. "Isn't your wife just gorgeous?" she says to the man.

"She is," he says.

"I could teach you a thing or two," Susan whispers into the blond's ear. "Do you want to come back there with me?"

And with that, all three of them slowly make their way to the backroom.