World's priciest home a true modern palace

"What we noticed in the last two years is that the most rapidly appreciating property prices are at the top end of the market," Knight Frank's Bailey says. A main reason is simple supply and demand, he says. A wealthy buyer of a house in London wants to be in an area like Mayfair or Kensington, already mature neighborhoods.

"The number of properties doesn't grow, but demand can double or treble over a couple of years," he says. "These are discretionary purchases; these aren't necessary. If they want it, they will pay what it takes to get it."

The home once again at the top of our list is Updown Court, a spanking-new palace in England. The residence has what one might call strong curb appeal, with 103 rooms, five swimming pools and a heated marble driveway. What it doesn't have is an owner in residence, as it was built on speculation in the hopes that a very wealthy, probably foreign, buyer will covet it.

The same goes in Palm Beach, where Donald Trump has put a massive oceanfront mansion on the market. It's gorgeous and grand, with marble floors and a conservatory that overlooks the ocean. But it lacks chandeliers and other details, because nobody has lived there since Trump bought it two years ago and began refurbishing it for the potential new owner.

As impressive as these homes are, just as rarified are the neighbors. That holds true whether you are in England (the queen of England's home, Windsor Castle, is near Updown Court) or in a seemingly far-flung place like Marrakech, Morocco. A romantic Art Deco tower nestled in the middle of a lush, private oasis is on the market for $10 million, tying for fourth place on our Africa list. Buy it and you can borrow sugar from the Hermès family or renowned and reclusive designer Yves Saint Laurent.

New properties are constantly popping up around the world--two impressive newcomers are in Istanbul, one for $100 million. But you will also see the same ones on our list year after year. Despite the expansion of Forbes' billionaires list (we found 793 this year, compared with 140 two decades ago), the number of people in the world who have the means to purchase a $100 million spread is quite small. And the subset of those who want a particular property with, say, views of the Bosphorus rather than the Atlantic Ocean, or done in the sleekest of contemporary styles rather than with gold leafing on the living room moldings, is even smaller. But fortunate, nonetheless.

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