Once the daydream of fantasy-prone sellers, the $100 million house is becoming, well, not commonplace maybe, but not so rare.”I’m at the point where I’m calling this a new category of housing,” says Jonathan Miller, chief executive of New York real estate appraisal firm Miller Samuel, Inc.”It is something that’s come of age in the past two years in response to global economic turmoil, where wealthy individuals are looking for ways to invest, and ultra-high-end real estate seems to be the asset of choice.”

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Two U.S. homes have broken past the $100 million threshold since the real estate downturn: a $100 million château in Los Altos Hills, Calif. that changed hands in 2011, and a hilltop estate in nearby Woodside, which quietly went for a staggering $117.5 million in November. Eight more listed with asking prices of $95 million and above are on the sale block, while several others, like financier Gary Winnick’s Bel Air manse, Casa Encantada (reportedly available for $225 million), are supposedly being shopped around as unofficial “pocket” listings.

What makes a home into a $100 million treasure chest? The iron rule of real estate comes into play, of course: A location in one of America’s most expensive Zip codes. In Manhattan that means a palatial spread in one of the most exclusive white-glove buildings bordering Central Park, like the Pierre Hotel, where the triplex penthouse co-op is listed for $125 million. In Los Angeles it means a coveted address on one of the guard-gated streets of the Platinum Triangle (Holmby Hills, Bel Air and Beverly Hills).

A prime piece of land is necessary, particularly in an area where abundant acreage is hard to come by, like the expansive 47-acre De Guigne estate in Silicon Valley’s Hillsborough. Offered at $ 100 million, it’s remained in the same family for the better part of 150 years. In the ritzy Mayflower Estates enclave of Dallas, Tex., where land commands $2 million an acre, the 25-acre Crespi-Hicks estate, designed by architect Maurice Fatio, can be yours for $135 million.

The homes themselves typically span 10,000 square feet-plus and pack in the kind of amenities produced when expansive imaginations meet bottomlessly deep pockets. Los Angeles’ $125 million Fleur de Lys manse boasts a 200-guest ballroom, a 50-seat home theater and a three-quarter-mile jogging track. Nearby, the Beverly House, once home to William Randolph Hearst, offers over 50,000 square feet of living space that includes two screening rooms, an art deco-themed private nightclub, spa facilities and a lighted tennis court with accompanying indoor bar. The Beverly Hills compound’s asking price, formerly at $95 million, was recently hiked to $115 million.

Equally important is the ownership lineage. A home tied to an esteemed public figure can offer unique bragging rights, even when the connection isn’t a happy one, as with Casa Casuarina, the $100 million Miami Beach mansion where Gianni Versace was murdered on the front steps.

“Homes of the trophy market aren’t simply defined by their price; they are unique properties that attract global interest,” adds Miller. As the number of billionaires in the world grows, so too does the possibility of more record-breaking real estate.”We will see more $100 million-plus sales in the coming years.”