There are other places in Manhattan that has trees besides Central Park. All you have to do is look up next time you are in Chelsea. Yes, The Highline is an above ground park built over an old train track. No trains have run on the Highline track since 1980. The Highline Park is probably one of the coolest recycled, renovated, eco-friendly spaces I have ever seen. It is free and definitely worth checking out next time you are in the city.
I found it kind of cool to turn this photo of a modern movie poster into an old timey looking photograph. The old architecture really adds to it.