When Howard Gleicher, a resident of the Orange County suburbs, decided to buy a four bedroom condominium in The Century, it was with a long-term plan in mind. Sure, the investment manager needed an immediate crash pad in Los Angeles to manage the increasing amount of time work was requiring he spend there; but he also wanted an apartment that would be big enough and luxurious enough to eventually move in full-time.

“I decided I needed to get ahead of the trend that I’m seeing, which is more people moving not only back into cities but into multifamily dwellings,” says Gleicher. “It’s because of the services they provide, the ease of living, the security.”

The 42-story Century, one of several high-rise luxe apartment buildings developer Related Coshas constructed in the past five years, touts a star-architect lineage (Robert A.M. Stern designed it), a double-gated security entrance and amenities like outdoor fireplace-bedecked dining rooms, wine cellar storage, and a fitness area with spa. The development got instant buzz in 2007 when Candy Spelling, wife of late TV producer Aaron Spelling and former owner of the $85 million Manor, snapped up a 15,600-square foot, $35 million penthouse – the most ever spent on a condo in Los Angeles.

“Security and privacy are the biggest requests from my clients,” says Bachir Oueida, president of L.A. Real Estate. He currently represents two units under contract in the building. “They don’t want to worry about finding someone trustworthy to take care of the garden or that somebody could jump the fence.” He says his biggest condo clients fall under one of two categories: wealthy international buyers in need of a pied-a-terre and single family homeowners looking for less hassle.

Gleicher joins an array of homeowners (like Spelling and Oueida’s clients), real estate experts and billionaire developers who believe luxury apartment living is the more secure, more convenient trend of the future. “That’s where the action has been,” says Jonathan Miller, chief executive of Miller Samuel Inc, a New York City-based real estate appraisal firm. “It [the ultra high-end apartment market] seems to have more of a higher concentration of activity,” especially in major metro areas like New York City. Miller tracks housing market activity in urban areas that include New York, Miami, and Washington D.C.

In Manhattan, a market dominated by condo and co-op properties (townhouses make up a mere 2% of activity), 2010 and 2011 saw more sales for three and four-bedroom apartments than any other years in the decade proceeding them, according to data from Miller Samuel and Prudential Douglas Elliman. In other words, homebuyers have been picking up large units in high rises, opting for city dwelling over the more traditional suburban, standalone home experience that has defines Westchester County and Long Island.

“People that used to think city living was too edgy, consider it to be an extremely safe environment now,” says Gary Malin, president of Citi Habitats, a New York City-based realty firm. In conjunction with Corcoran Sunshine Marketing Group, Malin’s firm represents new luxury high rises like The Aldyn on Manhattain’s Upper West Side, that cater to families with larger layouts and kid-friendly amenities like a bowling alley. “I think that they feel the conveniences outweigh the commuting time that would otherwise be spent.” So as more high rises dapple city skylines, more humongous apartments become available.

Sorting through thousands of high-rise condo and co-op listings from around the U.S., we picked out the most opulently adorned and the most spacious offerings, ranging in size from 4,000 to 17,000 square feet. Every property has a price tag of more than a million dollars, and each sits atop a tall, amenity-laden multi-family building. Sotheby’s International Realty, Coldwell Banker Previews International, the Corcoran Group, Realtor.com, Zillow.com, and others helped us compile our list.

The biggest apartment on our list is a $35 million penthouse apartment in Miami, Fla.’s Continuum South Tower. The palatial 11,031 square-foot pad spans four levels overlooking Miami Beach and the surrounding city.  It boasts separate a separate, detached guest loft and an additional 6,000 square feet of outdoor space that includes a sundeck and a private pool.

Another established Miami building, Acqualina, is known for its five-diamond boutique hotel and posh apartments overlooking the Sunny Isles beaches. But the Trump Group now plans to roll out an additional tower housing 79 mega condos referred to as “sky mansions.”  Ranging in size from 4,600 square feet up, the “mansions” will boast full outdoor kitchens and private custom outdoor hot tubs. The biggest unit – priced at a staggering $50 million — will encompass 16,000 square feet that includes seven bedrooms, a 25-foot home theater, a library, a private pool, and a hot tub with massaging waterfall.

“We have people interested in that penthouse,” says Michael Goldstein, Acqualina’s director of sales. “It’s a house. It’s like having your backyard and your front yard but they are 65 stories up – literally.” He’s probably not exaggerating. The most expensive condo sale in Miami ever was the Setai penthouse in December for $21.5 million, or $3704 per-square-foot.