But then, so are the cantilevered terraces, the bridge over Bear Run, even the trees.
Yes, one of the world's most famous houses can now be yours, all 811 pieces of it.
"It'll keep you busy for a while," said Adam Reed Tucker, the Chicago architect who designed the 10-inch-long, 6-inch-high LEGO replica of Fallingwater last year.
Mr. Tucker's company, Brickstructures Inc., teamed with the LEGO Group to produce the new Fallingwater set. Retailing for $99.99, the kit also includes a 100-plus-page spiral-bound book with assembly instructions as well as drawings, photographs and a history of the Fayette County house that Frank Lloyd Wright designed in 1935 for Edgar and Liliane Kaufmann.
Mr. Tucker was at Fallingwater yesterday to promote the model, which debuted at Manhattan's Guggenheim Museum in May, along with his LEGO replica of that Wright building. The release coincided with the museum's current exhibit of Wright's work, marking the Guggenheim's 50th anniversary.
Each of Mr. Tucker's models -- there are six so far -- uses only stock parts.
"It's almost like a puzzle or Rubik's cube, trying to figure out which ones that LEGO makes best captures the design," he said. "It's nothing that someone else couldn't do, but I do take certain liberties. There's a borderline between getting something too cute or too realistic. I'm trying to look at it from a sculptural point of view."
Mr. Tucker studies photographs and architectural drawings of the buildings he miniaturizes but doesn't make any drawings himself before beginning a structure. He "scratch-builds" on the fly until he gets it right. In the case of Fallingwater, that meant 13 revisions. Mr. Tucker wanted it to be "interactive"; after it's assembled the house comes apart in five sections, revealing different floor levels. Depending on skill level, the kit should take between one and four hours to complete.
Mr. Tucker, who is 37, was 4 when he got his first set of LEGOs. He played with the plastic bricks until he was 14, then put them aside. After college, as a practicing architect, he did residential work for a decade.
"I did some neat projects and worked for some pretty neat people," Mr. Tucker said. "Then about 2004 I had this idea to do something different with my life."
Inspired by the events of 9/11, the Chicago skyline and his desire to combine his two passions, architecture and art, Mr. Tucker went to Toys-R-Us and filled about 17 shopping carts with boxes of LEGOs.
"I spent a small fortune," he said.
He brought them home, dumped out all the parts and started to build. With tens of thousands of tiny bricks, tiles and plates lying about -- they've taken over his seven-room townhouse, sparing only the master bedroom at his wife's request -- he began to create what he calls "a subconscious library in my head of the different colors and components."
After the World Trade Center collapsed, "people were intimidated by skyscrapers," said Mr. Tucker, who wanted to present them in a fresh, approachable way for people of all ages.
For the LEGO Architecture series, Mr. Tucker designed the Sears Tower, John Hancock Center, Empire State Building, Seattle Space Needle and the two Wright buildings.
He also has created a series of larger LEGO replicas -- up to 10 feet tall -- of the Sears Tower (recently renamed the Willis Tower), Empire State Building, St. Louis Arch and other landmarks, which can be seen on his Web site, Brickstructures.com. They are now on view, through March 15, 2010, at Chicago's Museum of Science and Industry, except for the 5-foot-long Fallingwater model, which accompanied Mr. Tucker to the house.
The LEGO kit, said Fallingwater director Lynda Waggoner, is "just another way that Fallingwater is seen as an iconic building and is recognized worldwide for its significance."
In working with the LEGO Group and the Frank Lloyd Wright Foundation, which licenses products based on Mr. Wright's work, Ms. Waggoner said she and her staff "wanted to make sure that it's a reasonable replication of the house and that we can be proud of it."
Next, Mr. Tucker may tackle either Mr. Wright's Robie House in Chicago or another international landmark for the Architecture series, which is aimed at luring adults back to LEGOs.
"Children are already there," said Mr. Tucker, who until yesterday had never visited Fallingwater. He stayed in the guesthouse, up the hill from the main house.
"It's really humbling and cool to feel like I'm in the presence of Mr. Wright," he said. "Last night I was the only one here. It was just me and the house. It's like it's not inanimate, but a living, breathing thing."