"The world's greatest party" is a sleepless juggernaut of music, masquerade, magic, and madness - a gargantuan spectacle in which the spectators are intimately involved. Where to start? First, there's the magnitude.

Although the official holiday lasts only four days, almost nothing else happens for a week. Traffic comes to a halt and cabbies don't care; they can watch a beautiful girl - or boy - slither across the hoods of their cars. Thousands of transvestites parade in front of the Garota de Ipanema, and neighborhoods become rhythm machines as more than 600 block parties and street parades send up a cacophony of drums, whistles, triangles, and yelping instruments called cuicas.

At nighttime parades, Rio's rich and famous dance away in $10,000 costumes, while on the beach strolling samba bands attract throngs of writhing sequined bikinis. Helicopters spin overhead, broadcasting the event to a nationwide television audience concerned with nothing else.

Although the parades cater to a rich, mostly white crowd, on the streets Carnival has the role of great equalizer in Brazil's highly stratified society. The samba beat penetrates all social levels in Brazil; secretaries become feathered dancing queens for the week, while bankers jump into the musical fray with street sweepers and petty thieves. The celebration also equalizes the sexes, since in addition to being the world's biggest party, it's the world's biggest transvestite gathering. And no matter what kind of scene they're into, Carnival's 300,000 or so overseas visitors find language gaps and cold-climate reserve melting away in a whirl of confetti, sexual ambiguity, and Afro-Brazilian percussion.

Each samba school is determined to drive the crowd wild and win acclaim as the best sambistas in Rio. The audience, sensing correctly that it's part of the show, responds to the visual and auditory rhythms with singing, hugging, and a massive free-form dance frenzy. Inside and outside the Sambodramo, the exuberant, infectious, and all-consuming fever is everywhere. In halls and streets packed way past capacity, all sense of decorum has long since evaporated into an orgy of dancing, singing, and exhibitionism, driven past all limits by the primal power of the samba beat.