When Bill Detweiler, an avid gardener, moved from Manassas to a condominium in Fairfax County, he left behind a Cape Cod house, a spacious yard and a garden.

What did he get in return? Acres of land, enough flora and fauna to fill an Audubon field guidebook, and a corps of landscapers to do all of the planting, pruning, seeding and weeding.

Residents of River Towers, including Detweiler, call their condominium complex "the best-kept secret in Washington." Some might scoff at the notion: How could three nine-story, T-shaped hunks of brick that seemingly eclipse the sun be a secret?

Try 26 acres of land and more than 500 trees that camouflage the elephantine buildings.

"When you drive down the [George Washington] Parkway to River Towers, you can just feel yourself decompress," said Melanie Wallace, the recently elected president of the condo association at River Towers, which is a few blocks off the parkway about a mile and a half south of Old Town Alexandria. "All you see are trees, flowers and the river. It's heaven."

Touring River Towers is like flipping through a landscape design textbook, with each page offering a different concept or theme. Manicured lawns curve along the bases of the International Style buildings, softening the hard, straight lines. In the summer, bright impatiens add some cheer to the facade.

Just beyond the tennis and basketball courts, cattails poke up from the marshland, home to beaver, deer and fox. Over the canal and past the playground, a forest of maple, oak and pine trees shade picnickers when weather permits. The property ends in a bamboo forest, but not before you pass the community garden, where residents can dig their green thumbs into the 60-odd plots.

"We have to recognize what we have, preserve what we have and add to what we have," said Detweiler, a 13-year resident and chairman of the Landscape and Ground Committee, which recently added eight bluebird boxes to the property. "From the biggest tree to the smallest plant, we give it a lot of thought."

With that goal in mind, the group, one of six standing committees, published the "Guide to the River Towers Landscape." The booklet includes survey maps and an A (abelia, glossy) to Y (yucca, adams needle) glossary of each shrub, flower and tree. Each listing includes the plant's common and scientific name, height and width, and country of origin. Even objects not created by Mother Nature warrant a mention, such as UP (utility pole) and CS (concrete slab).

All of the attention to the environment has paid off: The National Wildlife Federation recently accredited River Towers' land as a wildlife habitat.

In addition, the well-cared-for trees have weathered the most inclement conditions, the only casualties being a few broken branches. And the Nature Night lectures, which cover such topics as bluebirds and bats, as well as the property walkabouts are drawing crowds.

Wallace even hopes to introduce Saturday morning nature walks around the canal, a hotbed of bullfrogs and turtles, to attract children who love all things slippery and slimy.

But while the residents fawn over the landscape from spring to fall, they don't hibernate come winter. "There's a real hum to this community," said five-year resident Martha Bitar, 59. "No one stays in their apartment. There's so much intermixture."

Neighbors organize social events, such as bridge night, bingo, Oktoberfest and the Tanglewood Festival, which kicks off the spring planting season in the community garden. Even the on-site cat sitter, Anna Wittauer, plays host on occasion: On a recent Saturday morning, the 10-year resident was decorating the social room with Hello Kitty party favors for a potluck dinner and cat-tales swap. With 33 "clients," she was expecting a strong turnout.

River Towers wasn't always a quiet, homey place to live, where often the only sounds are chirps and croaks. In its previous incarnation as rentals, the property, built in 1963, was derisively known as the "Stew Zoo," due to its high number of tenants who were based at what's now Reagan National Airport -- a rowdy crowd of pilots and flight attendants with a partying streak.

Life at River Towers, however, calmed in 1984, when the buildings were converted into condominiums and a more mixed crowd starting moving in, including young married couples and retirees.

As at many condo complexes, many River Towers residents move on to buy houses, but just as many seem to stay put and simply upgrade to bigger units. With 525 units and seven floor plans to choose from -- ranging from 428-square-foot one-bedrooms to 1,362-square-foot three-bedrooms -- there are homes to fit varied tastes and budgets.

Deb Marten and her husband, Tim Byland, for example, own two units: a one-bedroom they rent out and a three-bedroom where they live. And though Byland admits that he has "always had the urge to have his own yard," the couple still say they appreciate River Towers' environment as much now, more than a decade later, as when they moved in.

Marten said she has always been "in awe" of the stately baldcypress tree she can see from her home. "I still feel like a newlywed. Even after living here all these years, I am still taking pictures of the place and the trees outside my window."

River Towers residents Richard and Bridget Wells walk their dog, Biscuit, in front of the condominium complex in Alexandria.