Every year, 10 million people stream through the Parc de la Villette, a 136-acre spread on the northern edge of Paris. But not many Americans know about Villette. That's partly because it is nowhere near the customary tourist sites. There's also nothing like it back home--or anywhere else, for that matter.

You won't find prim flower beds, topiary or reflecting pools in this immense urban playground. Picture instead one of the biggest, boldest public works in modern France--an oblong stitched with bike paths, concept gardens, cinemas, exhibit halls, circus tents, cabarets and cafes. A walkway topped by a jaunty undulating roof runs north to south, and cutting across this spine is a placid man-made canal. At the center, resting in front of the largest science center in Europe, is the Geode, an immense, glittering, steel ball that contains an Imax theater with a 1,200-square-yard screen.

Add dogs, in-line skaters, Frisbee players, skateboarders and bongo players, and aim yourself toward a bewildering array of attractions that includes playgrounds, bamboo thickets, a dragon slide with a 262-foot tongue, a beached submarine, carousels, canal boats and more pelouses authorisees--lawns you can actually sit on--than anywhere else in Paris.

But first, grab a map.

You could spend half a day here and do nothing but walk around. Or you could take in a show, listen to music, even visit a library--"intelligent leisure," in the words of Marie Vag Lugosi, who directs guided tours.

The president of the Villette, Bernard Latarjet, calls his back yard a "big cultural campus," but "multicultural" might be more apt. In July and August, the open-air cinema features Hollywood classics. Photo exhibits typically reach toward forgotten corners of the world like Siberia; this spring, the Villette hosted an interactive exhibit on immigration that had visitors assuming roles as desperate refugees. Theater, acrobatics, dance, jazz and rock-and-roll here are all as likely to be foreign as French.

The park's Grande Halle, a state-of-the-art industrial design when it was built in time for the 1867 World's Fair, is an airy steel-and-glass structure (282 feet across, 790 feet long, lofting to 62 feet) akin to the ones that housed Paris's food markets at the former Les Halles. It recalls a time when the urban planner Baron Haussmann was tearing up half of Paris to make it more streamlined and sanitary, and he devised the Grande Halle and an adjacent lion fountain to serve as feedlot and watering hole for its first central meat market.

The slaughterhouse was torn down to make room for Science City, which opened in 1986. Today, with 3 million visitors annually, it serves as the Villette's focal point, with a planetarium, interactive exhibits and optical effects.

Even jaded museum-goers are bound to enjoy the nearby Cinaxe, which offers virtual reality in the form of moving pictures--and moving seats--not to mention the Imax theater in the Geode next door.

Designed by the Swiss-French architect Bernard Tschumi and united by a grid of 25 lipstick-red "follies," the Villette has plenty of lawn, but you don't see it at first because of the expanse of urban cobblestone at the entrance. Tschumi laid down beeline paths to key attractions (the one that heads toward the Zenith rock-concert hall is tree-lined, like a road leading up to a rural chateau), and he linked a series of gardens with a wavy walkway designed to look like a piece of casually strewn movie film. But his use of visual puns isn't apparent at ground level. The best way to share his vision, indeed, would be to enter from the sky.

Without walls, doors or gates, the Villette is open to all, forming a porous membrane between city and suburb. The park is policed around the clock and, in a brilliant preemptive maneuver, a private youth association has hired teens from the edgy, multicultural neighborhood around Villette to guard the park against graffiti and other petty vandalism.

Considering the crowds, crime rates are remarkably low. Families can safely divide up, with adults, for example, attending an acrobatic display on one side of the park while older kids attend a rock concert on the other. At night, paths embedded with lights lead to the logical meeting place, the lion-rimmed fountain between the Grande Halle and the chic Cafe de la Musique.

For those more accustomed to gated bits of manicured nature set neatly into city blocks, the Villette's open-door policy can be jarring. "Parisians are used to fin-de-siecle gardens, where one must forget the city," explained Vag Lugosi. "Here, for the first time, we recognize it."

The Parc de la Villette is in Paris's 19th arrondissement (Metro: Porte de Pantin). In July and August, every day but Monday, you can arrive by boat (weekends only April-June and September-October): Exit from the Metro at Stalingrad, walk to the foot of the Boulevard de la Chapelle, cross the intersection, walk in front of the Rotonde de la Villette, take the staircase up to a footbridge, cross the canal and buy a $1.50 ticket for the Canauxrama navette, or canal jitney. The boat discharges passengers in the middle of the park, next to an ornate carousel.

Admission to the park, which is open from 6 a.m. to 1 a.m., is free; to the Geode, $9; to Science City, $7.90. A combined Geode-Cinaxe ticket is $13.75. Information: 011-331-40-03-75-03.

CAPTION: Children (left) play in the Parc de la Villette, a futuristic spread on Paris's north edge that attracts lots of visitors but little publicity.