From the beginning of the last NYC condominium boom up to today, Manhattan condos have been locked in a strange and occasionally silly sort of arms race. It's not one that puts anybody's lives at risk, thankfully -- this sort of arms race pertains mainly to amenities, and which condominium can have the biggest and best extras to go along with those condos for sale. It makes a certain type of sense, given that there are only so many ways that one luxury condominium for sale can differ from another luxury condominium for sale. And so we get the spectacle of The Aldyn with its 40,000-square-foot fitness center and the Cipriani Club Residences' 20,000-volume library and 20 Pine's private subway entrance. These are all nice things to have in a condominium, of course, which is why the aforementioned rank among the most popular Manhattan condo listings at New Construction Manhattan. But the appeal of those elaborate amenities is a bit more abstract than the simple joys of one of Manhattan's rarest and most sought-after amenities -- a private terrace.

The important thing to know, here, is that there's a big difference between a balcony and a terrace. A balcony is that small shelf of space you see hanging off of numerous Upper East Side luxury condominiums and Upper West Side condos; balconies tend to be smallish, with enough room for a couple of bikes, a pair of chairs, or whatever else doesn't quite fit in the apartment. A true terrace is a different thing entirely and, as Vivian Toy writes in The New York Times, it is a thing of beauty, and surprisingly rare.

"A recent search for perhaps the most unusual kind of outdoor space — a terrace or garden larger than the apartment proper — produced only about two dozen examples," Toy writes. "They ranged from a $12.5 million penthouse with 3,000 square feet of terraces to a $289,000 studio with a 400-square-foot garden. Brokers say that outsize terraces call out to a special breed of buyer. Outdoor space can drive up the apartment’s price and make it harder to sell in a down market, but it adds a distinctiveness that can help the property maintain its worth." That perhaps explains the slight but notable uptick in popularity for NYC apartments with terraces -- just 19% of Manhattan apartments sold in 2000 had terraces, while apartments with terraces comprised 23% of Manhattan apartment sales in 2010. The demand is certainly constant. After all, while everyone appreciates the convenience of an on-site fitness center (or a 20,000-volume library, or a private subway entrance), a terrace offers something no other Manhattan condominium amenity can -- a little bit of green space in the middle of Manhattan.