WHEN JIM and Holly Johnson extend an invitation for drinks or dinner, offering up their address is just a formality. It is far more to the point to say, "It's the pyramid house."

And you would respond, especially if you lived in the Midcentury Modern gold mine that is Seattle's Inverness neighborhood, "Oh, that house."

Welcome to tomorrow's house from yesteryear, the Century 21 Idea House, designed in conjunction with the Seattle World's Fair in 1962 and celebrated here today as the fair's 50th-anniversary celebration draws to a close Oct. 21.

The Johnsons' house (they are its fourth owners) was built in a cooperative effort by House & Garden magazine, the Georgia-Pacific Corp. and Seattle architects Fred Bassetti and Jack Morse.

The August 1962 issue of House & Garden (the home photographed by noted architectural photographer Ezra Stoller) touted it as built to sell for less than $35,000, offering seven "well-proportioned" rooms, two bathrooms, a powder room, three porches, two-car garage and a good-sized paved terrace "all wrapped in imaginative design and superb craftsmanship." Its peaked and shingled roofs defined the major zones of family activity, which radiated out from a central T-shape.

But the years do take their toll. And, since they bought it for $375,000 in 1990, the Johnsons have worked both to honor the Idea House's intent and to keep their 2,800-square-foot home modern.

"It had been rode hard and put away wet," Holly says. Still, they were attracted. Fabulous bones, large windows to Lake Washington; a house that could hold 100 for parties. "I think it was the funkiness; the pyramids on the roof," Jim says.

Shortly after buying, the couple contacted Morse. "He told us that when designing in the early 1960s you wanted as much of the square footage in the public spaces as possible," Jim says. "Totally opposite of how houses are designed now with big bedrooms and bathrooms."

Then they called architect Charlie Vos of Sortun Vos Architects. He added enclosures, laid new floors, remodeled bathrooms, the kitchen and family room, enlarged the master bedroom.

Work over the years is recalled by holidays: "That was the Valentine's Day Jim gave me a chisel," Holly says of the master-bedroom remodel.

There are also new double-paned windows. The central pyramid, a skylight, was reduced from four points to one, 8 feet by 8 feet. (Other pyramids feature redwood ceilings with clerestories, drywall in the bedrooms and family room).

Two years ago the Johnsons took after the patio. Landscape architect Brooks Kolb melded the Japanese garden feel (azaleas, stone lantern, fountain) and the house's modern theme (large stone pavers in charcoal and light gray, outlined in bluestar creeper, a coral bark maple underplanted with chorus grass).

And now time has come around again for the bathrooms. It takes a village, "and a lot of money," laughs Jim's sister, Kate Norgaard. They are all World's Fair kids. Norgaard's popped over to show off her Jim Beam Space Needle decanter and her jingly and still shiny World's Fair charm bracelet.

Over the neighborhood's Midcentury rooftops lies Lake Washington. Over the hill is Sand Point Country Club, reached by family golf cart.

Some years after the Johnsons bought the Idea House, architect Morse rang their doorbell. He handed Holly house plans. She gave him a tour.

"I think we take the design features for granted," Jim says. "But it's fun to see other people see it for the first time. It takes me back."

Rebecca Teagarden writes about design and architecture for Pacific NW. Benjamin Benschneider is a magazine staff photographer.