More than 4,000 creatures reside at this celebrated and influential zoo, operated by the Zoological Society of San Diego. The Society was founded in 1916 with a handful of animals originally brought here for the Panama-California International Exposition (many of the buildings you see in surrounding Balboa Park were built for that fair). Legend has it that the zoo's founder, Dr. Harry Wegeforth, a local physician and lifelong animal lover, once braved the fury of an injured tiger to toss medicine into its roaring mouth.

In the early days of the zoo, "Dr. Harry" traveled around the world and bartered native Southwestern animals such as rattlesnakes and sea lions for more exotic species. The loan of two giant pandas from the People's Republic of China in 1996 was a twist on the long-standing tradition: Instead of exchanging exotic species, the San Diego Zoo agreed to pay $1 million annually for the pandas, to aid conservation efforts in China (see "Panda-monium" sidebar below). The 100-acre zoo is also an accredited botanical garden, lavished with more than 700,000 plants. Dr. Harry brought home plants from every location where animals were acquired, ensuring what would become the zoo's naturalistic and mature environment. The species of flora from a variety of climate zones are said to be worth more than the animal collection, and in many cases (such as the eucalyptus for the koalas) the plants also serve as the primary diet of the animals.

The giant pandas may be the marquee attraction, but the zoo has many other rare and wondrous species: Buerger's tree kangaroos of New Guinea, long-billed kiwis from New Zealand, wild Przewalski horses from Mongolia, lowland gorillas from Africa, and giant tortoises from the Galapagos. The Zoological Society is involved with animal preservation efforts around the world and has engineered many "firsts" in breeding: It was here that the Anegada iguana was successfully bred in captivity for the first time, and where a home for a captive-breeding group of the recently discovered Visayan warty pigs was created.

Of course, the zoo's traditional beasties--lions, elephants, giraffes, tigers, and bears--prowl around as well, and a diverse collection of tropical birds is experienced via sprawling walk-through aviaries. The zoo was a forerunner in creating bar-less, moated enclosures that allow animals to roam in sophisticated environments resembling their natural habitats. The most recent of these is Absolutely Apes, a habitat that opened in 2003 to showcase orangutans and siamangs of Indonesia; it marks the first time these primates of a single ecosystem will share an enclosure at the zoo. This exhibit's debut also marks the first stage in the ongoing $26 million "heart of the zoo" project, designed not only to enrich primate and other quarters but to improve human traffic flow in the most congested part of the zoo. In addition to the Panda Discovery Center, other highlights include Ituri Forest, which simulates a central African rainforest teeming with forest buffalos, otters, monkeys, and shy okapis; Tiger River, a steep gorge with lush enclosures for fishing cats, tapirs, and tigers; the Polar Bear Plunge, where you'll find a 2.2-acre summer tundra habitat inhabited by Siberian reindeer, yellow-throated martens, and diving ducks, along with the titular heroes; and the Children's Zoo, which features a nursery with baby animals and a petting area where kids can cuddle up to sheep, goats, and the like. There's also an entertaining sea lion show at the 3,000-seat amphitheater (though this is easy to skip if you're headed to SeaWorld).

My favorite way to experience the zoo is to spend the day on foot navigating the lush canyons and dry mesas that bisect the facility. But if a lot of walking--some of it on steep hills, some of it quite exposed to afternoon sun--isn't your passion, the zoo offers a 40-minute guided bus tour that provides a narrated overview and covers about 75% of the facility. It costs $10 for adults, $5.50 for children 3 to 11, and is included in the "Best Value" admission package. You get only brief glimpses of the enclosures, and animals won't always be visible, so you'll be enticed to revisit some of the areas. Included in the bus ticket is access to the un-narrated Express Bus, which allows you to get on and off at one of five different stops along the same route. You can also get an aerial perspective from the Skyfari, which costs $2.50 per person each way. The ride lasts about 5 minutes--but it's better for a bird's-eye view than it is for spotting creatures. I recommend taking the complete bus tour first thing in the morning, when the animals are more active (waits for the bus tour can top an hour by midday). Ideally, after the bus tour, take the Skyfari to the far side of the park and wend your way back on foot or by Express Bus to revisit animals that you want to see.

In addition to snack bars and fast-food options, the zoo has Albert's, a beautiful restaurant at the lip of a canyon and named after the zoo's most famous ape. It's located behind Gorilla Tropics, and although the food is unexceptional, Albert's is a lovely place in which to break up the middle of the day (when the animals are laziest).