Who doesn't think they know Brazil's magic city of beaches, samba, and Carnaval? Rio de Janeiro is all that, of course, and much more. Pico Iyer uncovers a tropical megalopolis whose moods and colors change by the hour

By eight in the morning, the crowds are already beginning to form, huffing and puffing along the gorgeous strip of coastline that curves around Ipanema's two miles of beach. Old men in thongs and bathing trunks, wrinkled women in two-piece swimsuits, power walkers jutting their elbows back and forth as they waddle along the concrete—they're all in evidence on this buoyant midwinter morning, when (because it's Sunday) half the wide boulevard running along the most picturesque beach near central Rio is closed to traffic. A nun, with more clothes on than the rest of the dawdlers combined; a roller-skating mom pushing along a pram as she glides among the near-naked bodies; a man on a bike with speakers attached to its handlebars so he can blast his enthusiasms to the crowd—all of them are contriving to turn the stretch of pavement into a neighborhood gathering of sorts. Air kisses, hellos, rumors: "What's happening to Fernando?" "Did you see Cristina?" To a yapping dog: "Sit!"

The young are nowhere to be seen, still claimed by the night before, and to the north, a few minutes' walk away in Copacabana, two fishing boats are bobbing listlessly on the water. But here in privileged Ipanema, bronzed men who might be the brothers of Picasso are diving into the sand to retrieve a volleyballer's spike, and matrons are parading past as if serenaded by a new song entitled "The Old Girl from Ipanema." Age—or care or time itself (not to mention all the favelas in the hills)—is nothing that can't be wished away in free-and-easy Rio. In the tourist brochure I read over breakfast this morning, the back-page interview was with a cosmetic surgeon.

The carnival seems never-ending here, even in the fifty-one weeks of the year when mayhem is not official policy. And though Rio is perhaps the most underdressed urban center anywhere, it has worked hard to promote this nonchalance, bewitching the world (and more dangerously, the countryside around it) with images of the "Marvelous City." Display is Rio's currency, it's easy to feel, and shyness the only taboo. The day before, after I passed through immigration (at the only international airport I know of that is named not after a head of state or a fighter for social justice but a bossa nova composer, Tom Jobim), the first Brazilian to greet me was a young man in an old lady's unflattering dressing gown, hairy legs shown off to disadvantage, holding up a sign under his Bozo-red nose and bathing cap that read did you bring your swimming pool? (a catchy, if oblique, way to draw attention to the duty-free store nearby). Driving into the spread-out city from the airport—past bicyclists taking in the sun and joggers in the park, around the main lagoon—I'd seen clowns prancing in front of stores and figures on stilts waving their arms about on the sidewalks, adding their yellows and oranges to the tropical blaze.