By JOYCE WADLER


MARGARETVILLE, New York - “This is the chosen one,” John Carson says, standing in front of the boulder in the living room of his modern house high on a mountainside in the Catskill Mountains, northwest of New York City.

“This is the one that started it all.” “This” is the 230-metric-ton bluestone elephant in the living room: 2.4 meters high, 4.8 meters wide, 6.6 meters deep.

Since he was a boy, Mr. Carson, a New York City builder and real estate developer, dreamed of building a house around a giant stone. He and his wife estimate that they looked at 75 properties before finding this one.

“I said, ‘I want something massive , something bigger than would ever be appropriate.’ ”

Mr. Carson, who is 53, is the president of On the Level Enterprises, the real estate development firm that commissioned the Swiss-born architect Bernard Tschumi to design the critically acclaimed Blue building, a 17-story blue-glass residential high rise in Manhattan, which opened two years ago.

His dreams for the house, he says, go back to a walk he and his father took in the Allegheny Mountains of Pennsylvania mountains, when Mr. Carson was a boy.

“We had to walk past a creek and up into an area with a barn that probably hadn’t been used for 50 years,” Mr. Carson says. It “had fallen, dilapidated, over a huge face cliff. I was about 7 years old and I said, ‘Pop, someday I’m gonna build a house and the fourth wall is gonna be a rock.’ I looked for that rock for 40 years.”

Mr. Carson received a degree in art from Edinboro University of Pennsylvania, studied printmaking at Penn State and moved to New York in 1979, where he fell into contracting. He married Sharon Slowik, who works in textile design and essential oil therapy, in 1993.

In January 2003, a real estate broker showed them this piece of property on the side of a mountain in Delaware County. They hiked through the snow to reach it. There was no water, no electricity, only a hunting cabin and a rocky cliff. And of course the boulder, surrounded by ash trees. They paid $75,000 for 32 hectares.

Building around the boulder created questions to which, Mr. Carson learned, there were very few answers: Would the boulder act as a thermal heat sink? Would they be able to waterproof it against the stream of water than ran underneath the edge?

Nor was this a flat piece of property. The house would have to be built on two levels. Mr. Carson designed a home that was essentially two interconnected boxes on two separate foundations, with a steel superstructure.

New York City subway grating is used as a bridge from the second-level dining room to the living room and an outdoor deck. The cost was about $1,000. Isn’t it hard to find a subway grate? “Not for a New York builder,” Mr. Carson says.

As for the rock, not only has it never leaked, it maintains a temperature of 20 degrees Celsius throughout the winter. But that’s secondary to the thing Mr. Carson always suspected: “There’s just something inviting about being able to rub against nature in your living room.”