Every day of the year you can walk the grounds of the National Zoological Park.

And every day that you do, chances are you'll notice something new about the place and the creatures inhabiting it: such as the funny way the orangutans hesitate before climbing out on the Orangutan Transport System (the overhead cables they travel from the Great Ape House to the Think Tank, where they show off their communication skills). You'll notice the regal indifference of African cheetahs as they sashay from one side of their "simulated savanna" to the other, and you'll spot the nests of 400 black-crowned night herons that decided (coincidentally?) that the zoo would be a fine place to call it a night after a full day of fishing on the Potomac River.

Make your own discoveries on the zoo's two guided paths, Olmstead Walk and the Valley Trail. From the Connecticut Avenue entrance, Olmstead, the less-strenuous route, winds past the cheetahs; the Panda House, home of the zoo's most famous residents, Mei Xiang and Tien Tien, two giant pandas introduced at the zoo in 2001; the Elephant House, home to young elephant calf Kandula, giraffes and slippery hippos; and the Great Ape House, home to a family of gorillas as well as those thoughtful orangutans. Expect goose bumps in the Reptile Center, where the gators are very much alive -- though they don't always look that way -- and the Komodo Dragons are the first to breed in Western captivity. Check out the invertebrates building if you're into mollusks; but certainly don't miss the lions and tigers. On sunny afternoons, these cats prowl the banks of the watery moats that separate them from your jugular.

Also beginning at Connecticut Avenue, the Valley Trail involves a little legwork but is well worth it. Aside from the glamorous bald eagles (should these guys really be in a zoo?) and ever-popular seals (Norman the sea lion never seems to tire of lapping his pool), the Valley Trail features creatures that are less famous but no less fascinating than their counterparts on Olmstead Walk. Except for a few small and restrictive cages, the wonderful Bird House works hard to provide its exotic residents with comfortable accommodations. Outside in the Wetlands exhibit, wood ducks and brown pelicans hang out beside the pedestrian walkways.

The zoo participates in the international Golden Lion Tamarin Conservation Program and has an outdoor free-ranging tamarins exhibit where these endangered Brazilian monkeys roam free and uncaged. If you walk past the exhibit and never see any tamarins, it's probably not because they've headed for the Woodley Park Metro: Their whereabouts are tracked electronically, and, truth is, with food, family and good times all found easily at the zoo, why head downtown?

Make sure to stop at Amazonia, one of the newest animal houses, where the zoo's efforts to present itself as environmental educator and watchdog are most evident. Visitors walk through a simulated rainforest among scurrying titi monkeys, brilliant-red macaws, two-toed sloths hanging overhead and lush bromeliads, plants that survive by functioning as floral water tanks. Amazonia may be the zoo of the future, offering the chance to gawk at unusual animals and even learn a thing or two about how minute forms of life, and entire ecosystems, are interdependent.

Both Olmstead Walk and Valley Trail have restaurants and snack bars and both are close to the zoo's paid parking lots, which fill up very quickly in the summertime.

-- William Yardley

For Kids:

This is a great zoo and one with which you're likely to become very familiar. Every child has his or her favorite animal, but some highlights are worth stressing. One is the orangutan exhibit, which permits the animals to swing on ropes and towers above the zoo's walkways, essentially outside of any enclosure. Another is the indoor Amazonia exhibit, which displays rainforest environments and creatures. Others include the cheetah conservation area and the new invertebrate house, which offers a number of hands-on displays and a wonderful, see-through ant colony (the volunteer docents here are especially accommodating to children who show an interest, possibly in an effort to redeem the boring reputation of most invertebrates). Try not to take in the whole zoo in a single visit; that's not good for anybody. On the way in, let each child pick two or three animals to visit, and get a map to plan an itinerary. Or agree to explore just an area or two on this visit. If you don't, you're setting yourself up for some tired and whining kids. You can rent wagons and strollers, and don't be reluctant to procure one for toddlers.

-- by John Kelly and Craig Stoltz

Words to the wise: With Metro, get off at the Cleveland Park station and walk south (downhill) to the zoo. When you leave, continue south (downhill) to the Woodley Park/Zoo station. If you're driving and plan to visit for the whole day, try to park in the lower lot (Lot D). It's an uphill walk to most of the animals, but that means it will be downhill when you're heading back to your car with weary youngsters in tow. Avoid Lot C if at all possible: You have to climb a narrow staircase to get to the animals. Lots A or B, near Connecticut Avenue, are good for quicker visits, providing easy access to the cheetahs, the panda, the elephants and rhinos, birds and hoofed stock. But if you're planning an all-day visit, the top lots require an uphill climb at the end of the day.

Notes: The animal buildings and Amazonia are open 10 a.m. to 4:30 p.m. (till 6 in summer, with exceptions posted). Panda feedings are at 11 a.m. and 3 p.m., and seal and sea lion training and elephant care sessions are at 11:30 a.m. on most days.

Food: Fast-food stands of the hot dog-hamburger-snowcone-and-soda variety are dotted throughout the zoo. Two sit-down restaurants, the Panda Cafe and the Mane Restaurant, have a wider menu. You needn't go hungry at the zoo, but it's safe to say that the really tasty food is reserved for the animals.