One hundred years ago, America's first zoos were built in Philadelphia and New York, with extra-thick bars to assure the public that wild lions, elephants, and camels would not escape and attack. Today it's the wilderness that seems under siege, so zoos have evolved into centers of learning and conservation biology. But they continue to drive us wild.

Last year more than 100 million people visited our nation's zoological parks. Not everyone is willing to ante up the $42 adult admission to Disney's new 500-acre Animal Kingdom in Orlando, with its African Safari ride and 2,500 performing "cast members," but most find themselves happily exploring a neighboring zoo. The following are 10 of the most animal-friendly wildlife parks, sure to free the beast within.

Zoological Society of San Diego
Perhaps the best place to view animals without trekking into the wilderness, the Zoological Society of San Diego is actually a zoo and a park, each worth its own day trip. The San Diego Zoo comprises 100 acres of tropical grounds and 800 species (including a pair of pandas on loan from China). The 2,200-acre Wild Animal Park, 32 miles northeast of the zoo, features several natural habitats and a Galápagos tortoise that must have been around when Custer was fighting his last battle. Visitors can view roaming herds of exotic animals from a five-mile-long monorail or by way of a walking safari. Designed to help breed endangered species, the park has seen some 20,000 creatures born within its borders—including 120 rhinoceroses—since it opened in 1972. Many of the zoo's younger residents hang out at the Petting Kraal.
San Diego Zoo, 619/234-3153; $16 adults, $7 kids 3­11. Wild Animal Park, 760/747-8702; $19.95 adults, $12.95 kids 3­11.

Arizona­Sonora Desert Museum, Tucson
You could walk the 1 1/2-mile loop trail around the Desert Museum for a while before you realize that this 15-acre protected landscape is also a zoo. So well integrated are the desert animals with their rock-and-brush habitats that it may come as a shock when you turn a corner and notice a mountain lion checking you out from a ledge, from behind a thick layer of glass. This garden of cactus, grassland, and mountain woodland is adjacent to Saguaro National Park West in Tucson, so the animals at this "museum" actually inhabit the surrounding ecosystem. You'll find javelinas, bighorn sheep, butterflies, Colorado River squawfish, beavers, Gila monsters, rattlesnakes, owls, and prairie dogs. It's impossible to come away from this experience without a newfound appreciation for the phrase living desert.
520/883-2702; $8.95 adults, $1.75 kids 6­12.

Minnesota Zoological Garden, Apple Valley
Twenty miles south of the Twin Cities, this zoological park has an enclosed tropical exhibition, the Coral Reef, with South Pacific lagoon creatures such as sharks, rays, and dolphins. But to take full advantage of the zoo you should hike the Minnesota Trail and the Northern Trail. Along these you're sure to spot the hardy wild animals of this state and of the world's Northern Hemisphere: fishers, lynx, woodchucks, wolverines, musk oxen, caribou, sandhill cranes, and Siberian tigers. The zoo is also part of the International Species Information System, a kind of computer dating service that provides stats on 5,700 endangered species; the data are traded among 54 zoos around the world.
800/366-7811; $8 adults, $4 kids 3­12.

Brookfield Zoo, Brookfield, Illinois
It's no wonder that the indoor exhibitions here are as extensive as the outdoor ones, given that in winter no living creatures except polar bears would be caught outside. For a landlocked zoo just 14 miles outside Chicago, Brookfield is quite marinelike, with "The Swamp: Wonders of Our Wetlands" exhibit, rainy Tropic World, the Peruvian and Chilean Living Coast, and the Seven Seas Panorama where walrus, seals, sea lions, and trained dolphins swim about.
708/485-0263; $6 adults, $3 kids 3­11.

St. Louis Zoo, Missouri
The naturalistic exhibitions here attract more than 2.5 million people each year, and now there's a children's zoo for younger devotees. Along with fuzzy koalas and dive-bombing lorikeets that will sip nectar from cups held up by squealing kids, the youngsters' zoo has a "Just like Me" play area, where children can dig like an aardvark in a sandbox or climb jungle vines like monkeys. The best part, though, is a transparent acrylic tube that runs through the otters' swimming hole; kids can slide down it and emerge in the viewing area below. The only drawback?No adults allowed on the slide.
314/781-0900; free.

Audubon Zoo, New Orleans
More than 1,500 critters, whose habitats span the globe, shelter in a park made famous by Paul Schrader's Cat People. Among the highlights are crowd-pleasing feedings and shows starring sea lions, elephants, alligators, and nutrias (a giant rodent considered a major pest in the swamps beyond the zoo). One of the few zoos to brag about its food (for humans), the Audubon even has a cottage selling spicy Cajun dishes as part of its Louisiana Swamp exhibit. There, cultural and natural history merge, so you'll also find a trapper's cabin and zookeepers feeding gators by hand.
800/774-7394; $8.75 adults, $4.50 kids 2­12.

Miami MetroZoo
The only wildlife park in the United States located in a subtropical climate, MetroZoo offers large, open-air exhibitions. While the Asian river otters, clouded leopards, tigers, giraffes, wallabies, and Komodo dragons seem quite pleased with the jungle-like weather, visitors, particularly in summer, should be prepared to sweat like warthogs (not that you can tell if a warthog is sweating). At the popular Ecology Theater kids can get an up-close look at south Florida's own animals, such as the American alligator, American crocodile, and gopher tortoise.
305/251-0401; $8 adults, $4 kids 3­12.

National Zoo, Washington, D.C.
If your kids are into giant, goat-eating lizards—and whose aren't?—then the National Zoo's Reptile Discovery Center is for them. You can watch Komodo dragons feed, even if no goats are tethered there. Meandering, tree-shaded paths lead to a range of animals, including Hsing-Hsing, the only giant panda on the East Coast, who emerges late in the afternoon to feast on bamboo and carrots. Another attraction is the overhead Orangutan Transport System, 400-foot-long cables that allow orangutans to swing above you on their way to and from the Think Tank, where the apes use touch-screen computers while scientists measure their comprehension skills. A full-fledged research center, the National Zoo also breeds a colony of golden lion tamarins (read: fuzzy orange monkeys). Members of this band are among the few zoo-bred animals ever to have been successfully released into the wild—in this case, Brazil's endangered Atlantic rain forest.
202/673-4800; free.

Bronx Zoo, New York
Visiting the largest urban zoo in America—with more than 6,000 animals spread across 265 acres—definitely calls for a daylong picnic plan. In recent years, the Bronx Zoo, formerly known as the Wildlife Conservation Park, has changed more than its name, building natural habitats such as JungleWorld and the Himalayan Highlands. These sites re-create places where the zoo's scientists have embarked on field conservation efforts. Our fragile world takes on new beauty inside the Butterfly Zone, opening in May, where visitors can mix with a blizzard of multihued insects. Hint: If you wear bright colors they're more likely to land on you.
718/367-1010; $7.75 adults, $4 kids 2­12.

Roger Williams Park Zoo, Providence
The third-oldest zoo in America, this gem has about 1,000 animals. Along with snow leopards, a cheetah, and bears, it houses an impressive bug exhibition whose star attraction is giant Brazilian cockroaches. If insects aren't your thing, stroll through the 438-acre Victorian park. It's just a short walk from the cheetah's enclosure to lakefront benches where you can relax and feed the ducks to the distant trumpeting of elephants.
401/785-3510; $6 adults, $3.50 kids 3­12.

DAVID HELVARG is a freelance journalist and author of The War Against the Greens.