It's hard to have secret places, in New York. There are so many people, everywhere, that nothing can really be hidden.
But you can, sometimes, have the illusion of being hidden. Which brings me to one of my favorite places: The High Line.
Once an abandoned elevated railroad, it is now one of the most popular parks in the city. It starts around 14th st and someday will stretch all the way up to 34th or so; it has opened in segments. Currently it's a narrow river of green running in an otherwise industrial landscape.
It's a tourist favorite, of course, and a good place to bring out of town visitors - it's self contained, there tends to be seating, and the people-watching is great (it's also a hot first date spot) - but the people who live here also use it. If you have to walk to work, why not walk under the trees and past the flowers? If I worked in Chelsea I'd probably spend all my lunch hours there.
The High Line
The World Outside