Then there is the $88 million crash pad at 15 Central Park West, bought last year by a trust linked to Ekaterina Rybolovleva, then 22 years old. Ms. Rybolovleva is the daughter of a Russian billionaire in the fertilizer industry, Dmitry Rybolovlev, who is in the middle of a rather expensive divorce. In a lawsuit filed last year, Mr. Rybolovlev’s wife, Elena Rybolovleva, alleged that the apartment was bought not as a place for their daughter to live, but as a way to put that money out of the older Ms. Rybolovleva’s reach. According to court documents, the younger Ms. Rybolovleva is a resident of Monaco.

The building at 15 Central Park West has its share of pieds-à-terre, real estate professionals say. But the concentration there is not as high as in other brutally expensive buildings, especially those in Midtown that share space and services with hotels, like the Plaza or the Time Warner Center, which shares a building with the Mandarin Oriental.

“I was living on the 16th floor, and I was pretty much the only one there,” said Charlie Attias, a senior vice president at the Corcoran Group who rented an apartment at the Plaza for three years and has handled many transactions in the building. “We had the occasional visitor — I mean, the occasional owner — once in a while.”

“Actually, when we saw somebody, it was a big thing,” he added. “Oh wow, somebody’s in my hallway!”

Scott Stewart, a senior vice president at the Corcoran Group, sold five condos at Time Warner Center over about eight years. He has had buyers from London and Hong Kong, Minnesota, New Jersey and Texas — and not a single one from New York. In all the times he has shown the building to prospective buyers, he added, he never saw more than one person using the condo’s gym at a time.

“I’ve seen Kelly Ripa there,” he said of the television star, who has since moved out. “Two little kids were playing with Legos on the treadmill next to her, and there was nobody else.”

Elizabeth Lee Sample, a broker at Sotheby’s International Realty and a member of the board that oversees the Time Warner complex, estimates that the condos in the south tower are generally about 60 percent occupied, while those in the north tower are only about 30 percent occupied, except during the holidays.