picture from nationalgeographic.com
The High Line is located on Manhattan's West Side. It runs from Gansevoort Street in the Meatpacking District to West 34th Street, between 10th & 11th Avenues. Section 1 of the High Line, which opened to the public on June 9, 2009, runs from Gansevoort Street to West 20th Street. Section 2, between West 20th and West 30th Streets, opened June 8, 2011.
You may find more information on the Highline website here.
Also remember to check the beautiful pictures on the National Geographic article "Miracle above Manhattan" here.