The house is off-limits to children, and adults are asked to sign a waiver when they enter. The main concern is the concrete floor, which rises and falls like the surface of a vast, bumpy chocolate chip cookie. But, for Arakawa, 71, an artist who designed the house with his wife, Madeline Gins, the floor is a delight, as well as a proving ground.

As he scampered across it with youthful enthusiasm, he compared himself to the first man to walk on the moon. “If Neil Armstrong were here, he would say, ‘This is even better!’” Then Gins, 66, began holding forth about the health benefits of the house, officially called Bioscleave House (Lifespan Extending Villa).

Its architecture makes people use their bodies in unexpected ways to maintain equilibrium, and that, she said, will stimulate their immune systems. “They ought to build hospitals like this,” she said. Like the undulating floor, Arakawa and Gins, as they are known professionally, tend to throw people off balance.

In 45 years of working together, they have made it their mission — in treatises, paintings, books and now built projects like this one — to outlaw ageing and its consequences. The house on Long Island, which cost more than $2 million to build, is their first completed architectural work in the US — and, as they see it, a turning point in their campaign to defeat mortality.

The house, which is still unoccupied, was commissioned in the late 1990s by a friend who sold the property to an anonymous group of investors after the project dragged on and costs mounted. But it is ready, Arakawa and Gins said, to begin rejuvenating whoever moves in. In addition to the floor, which threatens to send the un-sure-footed hurtling into the sunken kitchen at the centre of the house, the design features walls painted, disorientingly, in about 40 colours; multiple levels meant to induce the sensation of being in two spaces at once; windows at varying heights and an open flow of traffic, unhindered by interior doors or their adjunct, privacy.

All of it is meant to keep the occupants on guard. Comfort, the thinking goes, is a precursor to death; the house is meant to lead its users into a perpetually “tentative” relationship with their surroundings, and thereby keep them young. The architect Steven Holl, who has known the couple for at least 15 years, said their architecture is intended to evoke a youthful sense of wonder.

“It has to do with the idea that you’re only as old as you think you are,” he said. Don Ihde, a professor of the philosophy of science and technology at Stony Brook University and a friend of the couple, described them as provocateurs. Their work “makes people think through what they wouldn’t normally think through,” he said.

Lawrence Marek, a Manhattan architect who helped steer the house through the construction process, disagreed. “Arakawa does believe that if you build things the way he says to build them, life will be prolonged,” he said. “I don’t know if it will or not.” But, he added, “the house has a way of making people happy — it’s a feeling you don’t get from many buildings — and we should be studying how that happens.”

Arakawa grew up in Nagoya, Japan, studied medicine and art in Tokyo, and moved to New York in 1961,when he was in his 20s. Two years later he enrolled in art school in Brooklyn. There, he met Gins, a fellow student,who had grown up on Long Island. At the time, she said, “I was deeply alienated from society,which I didn’t see as having any answers.

”Within days they had become a couple and begun making art together. Over the next several decades, living in a loft building on Houston Street, they produced a body of work that includes poetry, philosophy, paintings and conceptual art. From the start, Gins said, the central theme of their work was “how to reverse the downhill course of human life.”

For the couple, “one building is worth a decade of theoretical exploration,” Gins said. Arakawa and Gins persuaded companies to donate what they said were hundreds of thousands of dollars’ worth of materials and products to the house. George Bishop, president of Get Real Surfaces, in New York, which fabricated counters, tabletops and an elaborate bathtub to the couple, charged about a tenth of the usual cost, he said, because he was so taken with them.

Part of their appeal, certainly, has to do with their unwavering conviction. Gins speaks passionately about their work, while Arakawa tells charming if immodest anecdotes about their triumphs. Now they are determined to conquer architecture.“We should win a Nobel Prize for this,” Arakawa said. Asked if her husband was serious, Gins replied, “Of course he is."