FAMILIES in Richmond have one more gift to be thankful for this holiday season: The long-awaited opening of the Robbins Nature and Visitor Center at Maymont. In the works for several years, the newly opened center is a state-of-the-art complex that houses multiple aquariums, interactive educational exhibits and a spectacular 20-foot waterfall. Maymont has long been a popular family destination in Richmond, and the Nature Center provides one more reason to visit.

Maymont is 100 acres of idyllic rolling parkland right in the heart of Richmond, an oasis two miles from downtown. Constructed at the turn of the century, Maymont was the country estate of Richmond financier James H. Dooley and his wife. The Dooleys, who had no heirs, willed the land to the City of Richmond in 1926, intending that it become a public park and museum. There is a 33-room Victorian mansion on the grounds (the former Dooley residence, restored to its turn-of-the-century splendor), as well as formal Italian and Japanese gardens, an arboretum and a children's farm and petting zoo. All attractions are free and open to the public, including the Robbins Nature and Visitor Center.

Stepping inside the Nature Center is like entering another world. The focus is on one of the area's greatest resources, the James River -- Richmond is known, after all, as "the River City." In the entrance gallery there are photographs of the James, from kayakers shooting its rapids to placid, reflective scenes. Follow the gallery walkway a little further and you will see and experience the river in ways you could never have imagined.

You can hear the flowing water long before you see it: the distinctive roar and splash of a 20-foot high waterfall. The photo gallery opens to a brightly lit vista where a cascading indoor waterfall stands as a stunning centerpiece. Water pools at the base of the falls and then flows into an intricately designed series of linked aquarium tanks, a 125-foot-long display replicating one continuous body of water: the James River.

The 13 tanks that comprise the habitat series are integrated with rocks and trees and other indigenous vegetation, making it appear that the river is cross-sectioned, bisected to allow visitors a look beneath its banks. "This is a glimpse of the river like you've never seen before," says Nature Center Director Mark Rich. "This is a chance, the opportunity, to see the world below the surface."

The first thing you notice about this underwater world are the fish. There are hundreds of them. As you follow the trail of tanks, you follow the path of the river. Along the walkway you travel past different types of ecosystems including shallow pools, open water, backwaters, a turtle pool (with snapping turtles), estuaries and channel runs. Each aquarium section represents a different river environment with various species of fish, turtles and other animals.

One of the most popular tanks is home to two very active and playful otters. They are the unofficial mascots of the new center; otter hand-stamps are given at the entrance and signs emblazoned with otters lead the way to the Nature Center's front door. One of otters was rescued last spring from the Chickahominy River. The relocated animal seems quite at home in her new habitat, a large indoor/outdoor tank with plenty of room to maneuver.

The air in the Nature Center smells a bit damp and earthy. And with the fish and the sounds of birds -- yes, there are birds in the trees -- and rushing water, it's as if you're not indoors at all, but rather on the river bank. A completely transporting experience.

Not to give the impression that time spent at the Nature Center is simply for tank gazing. On the contrary, as you walk along the river path there are educational galleries to stop in and learn about the river. Almost all of the Nature Center's exhibits are interactive, with levers to turn, flaps to open and buttons to press. This is not passive learning. Participants see the river, then try their hands at displays that reinforce the different principles illustrated -- fish passages, locks and canals, uses for water and the importance of weather conditions. As a river city, Richmond is no stranger to high winds and flooding. In one exhibit, a marooned-looking television sits atop storm debris and rubble, showing historic video footage of past Richmond floods, an effective reminder of the power of the James River.

Education is the main purpose of the center; its mission is to promote good stewardship of nature. Along with the interactive exhibits, there are "Discovery Zones" that include the Discovery Room, the Discovery Lab and a comprehensive exhibit on the birds of the James River. The Discovery Lab is a place where children ages 8 and up can explore the natural world with the help of microscopes and other laboratory equiment. For younger children there is the Discovery Room, which offers many hands-on projects, including storytelling trees with movable figures and discovery boxes that contain surprises to explore. There is also a night gallery of sorts, for all ages, a reversed light exhibit space where you can get up close to study the behavior of nocturnal animals, with owls, meadow voles and white-footed mice on display.

"The river has so many connections," says Director Mark Rich. "It was a natural choice for us as an educational tool, with its links to animals, plants, conservation, water quality, and ecosystems. This is not just about our river, the learning here connects us to any river in the world."

Like other Maymont attractions, admission to the Nature Center is free, though donations are gladly accepted. For those planning to spend the day at Maymont, there are trams and horse-drawn carriages (in keeping with the estate's Victorian roots) to take you from one end of the 100-acre park to the other. Located inside the Nature Center is the new Maymont Cafe and the newly expanded Maymont Shop, a gift shop that specializes in educational games and toys. Much of the merchandise carried in the shop reinforces messages from the exhibit, with a variety of science kits, books and learning toys available. Though not all of the inventory serves such lofty purposes: It is reported that many of the shop's plush toy otters have found their way to good homes.

THE ROBBINS NATURE & VISITOR CENTER AT MAYMONT -- 2201 Shields Lake Drive, Richmond. Richmond is about a two-hour drive from the Beltway, via I-95 South. Take 95 to the Boulevard (Exit 78). Follow signs south on Boulevard/Route 161 to Maymont. 804/358-7166. Web site: www.maymont.org. The Nature Center is Open Tuesday through Sunday, 12 to 5. Free, but donations are welcome. The Maymont House, Children's Farm and Maymont Shop are all open Tuesday through Sunday from 12 to 5. Free. The Visitor Center, grounds and gardens are open daily from 10 to 5. Free. The Maymont Tram runs from 12 to 5, weather permitting. $2 for adults; $1 for children; free for Maymont members. Maymont Carriage Rides run on Sundays from 12 to 4, weather permitting. $3 for adults; $2 for children. (Available by reservation at other times.)