"That's what it sounds like when I scuba," says an adult to a child who is hugging and putting his ear to one of the see-through columns of bubbly water at the entrance to the National Aquarium in Baltimore. At the sparkling new facility on Baltimore's inner harbor, children not only get to look at sea creatures; they get some idea of what it might be like to be one.

"They look like they're having fun," says a child watching two bottlenose dolphins cavort in a 260,000-gallon pool. The pool, 18 feet deep, fills the central area of the building and visitors could watch the dolphins at play from all vantage points -- from above, reflected in ceiling mirrors and through underwater windows -- until they were moved away because their tank was leaking. But they'll be back, officials say, as soon as the tank is fixed.

"Dolphins talk to each other, you know," says a mother.

"I know," says her child. "They whistle through their blowholes to communicate."

After riding the escalator to the sounds of sea creatures, we are introduced to the idea of how water gets from the mountains to the sea. The journey begins at a pond in western Maryland, and an adult asks a child who can wriggle through the crowd to the simulated pond what creatures she sees.

"Plain fish," replies the child, meaning the likes of crappie, catfish and carp.

In a tidal marsh on the Eastern Shore there are minnows and crabs and oysters, and from the beach at Assateague we see weakfish (sea trout), snails and periwinkles and sandpipers. At journey's end, the Continental Shelf, the sea trout are bigger and share the habitat with dogfish and lobster.

There's a movie about humpback whales and other creature not in the aquarium, but the living, swimming animals are more fun. There are live, spontaneous demonstrations of the different ways sea creatures eat: some slurp, others filter or grasp or suck or pick. Other tanks show the different ways sea denizens move or hide or protect themselves, the Moray eels simply by displaying their fierce teeth.

On the stark sea cliffs of Iceland, puffins, murres and razorbills swim, socialize and eat a buffet lunch of fish scattered on the rocks. "I saw one eat a fish!" says an excited child.

There's also a kelp forest off the California coast and a Pacific coral reef populated by bright blue and yellow fish and, to enable us to get our land legs again, a rain forest, "a land-based environment where every form of life depends on water."

"Oh, it's hot here," says one child stepping off the escalator into the steamy Amazon Basin.

"It's supposed to be," advises her older sister, who has studied rain forests in school. Macaws, sloths and rodent-like acouchis pop out from the dense greenery, and turtles and Amazon Basin fish lounge in the ponds under the bridges.

From the forest, which is inside a glass triangle at the top of the building, we begin our descent on a ramp that leads us round and round and down and down along a half--5 million-gallon ring tank. First we are in an Antlantic coral reef, swimming along with hogfish and wrasse and butterfly fish. The fish all seem to be rushing in one direction and we finally spot the attraction: A man in scuba gear is in there with them and is dispensing a steady stream of little fish.

"I wonder where the hammerhead is now," says a boy, grinning gleefully.

Actually, the sharks are in the open-ocean tank, where they can't get at the reef fish, though scuba divers do get in with them three times a week to feed them. It's not feeding time, but the sharks, though not eating, still look menacing enough to attract masses of macho boys.

"Look at the lemon shark!" "Man, see that sting ray!" they shout as we plumb the depths of the tank.

In the Children's Cove, a simulation of the Maine coast, the inhabitants are less menacing but you can touch them as well as watch them. While a school group takes notes around a tidal pool and smaller children have fun just romping on the ersatz rocks, docents let kids get the feel of sea urchins, starfish and horseshoe crabs.

"That little hole is where it sucks in water," a docent tells a child who is gingerly holding a starfish. "Then it pushes the water out to move."

The child notices that the starfish is missing a leg, but the docent says not to worry.

"Do you know what happens when a starfish loses a leg? It grows another one," she assures the child.

Starfish sit still, but holding a horseshoe crab is another matter.

"Got him in both hands? He's going to wiggle now," another docent warns another child. After mastering holding the crab, which is turned on its back, the child decides to go one step further -- and lives to tell the tale.

"Mommy," she says in triumph, "I stuck my finger in his clutches and it didn't even hurt."

EXPERIENCING THE AQUARIUM

The National Aquarium is on Baltimore's Inner Harbor, at 501 East Pratt Street. Pay parking is available. You can also take Amtrak to Baltimore's Penn Station (be sure to ask for the family excursion plan if you're taking children) and then take a 62 or 64 bus to the Inner Harbor from St. Paul Street, just to the left of the station. Bus fare is 60 cents in exact change. The aquarium is open daily 10 to 6 and until 9 on Friday evenings. You may have to wait in line 20 to 30 minutes on weekends. Weekday mornings, the aquarium is often filled with school groups. Weekday afternoons and Friday evenings are probably the best times to visit. Admission is $4.50 for adults, $2.50 for children.

FEEDING TIMES: 10, 1 and 4 daily in the outdoor seal pool; 11:30, 2 and 4:30 daily for the dolphins; 11, 1:30 and 3:30 for the coral-reef fish, and 2:30 Wednesday, Friday and Sunday for the sharks and other open-ocean fish. For humans, the cafeteria- style Seal Harbor Cafe next to the seal pool offers hot dogs ($1.10), crabcake sandwiches ($2.50) and other fare. Be sure to have your hand stamped if you want to go back to the aquarium after lunch. Other attractions at the Inner Harbor include the U.S. Frigate Constellation, oldest ship of the U.S. Navy; the Top of the World, which affords a nice view despite the hyperbole, on the 27th floor of the World Trade Center; and, of course, Harbor Place, a collection of shops and eating places.