Bill Cunningham has a very cool piece about the elevated sidewalk in NYCity called the "High Line". Wikipedia calls it a "greenway." If you want to see his audio slide, click here. If I were going to NYCity any time soon -- you best believe that I would go to this greenway for a nice walk. [mumble mumble ... wish I were going ... ]
Here's an excerpt from the item in Wikipedia:
The High Line is a 1.45-mile (2.33 km) section of the former elevated freight railroad of the West Side Line, along the lower west side of Manhattan, which has been redesigned and planted as a greenway. It runs from the former 34th Street freightyard, near the Javits Convention Center, through the neighborhood of Chelsea to Gansevoort Street in the Meat Packing District of the West Village. The High Line was built in the early 1930s by the New York Central Railroad to offer direct warehouse-to-freight car service that reduced pilferage for the Bell Laboratories Building (now the Westbeth Artists Community) and the Nabisco plant (now Chelsea Market), which were served from protected sidings within the structures. It was in active use until 1980.To read the whole thing, click here.
In the 1990s, it became known to a few urban explorers and local residents for the tough, drought-tolerant wild grasses, forbs and trees that had sprung up in the gravel along the abandoned railway.
By 1999 broadened community support of public redevelopment for the High Line for pedestrian use grew, and funding was allocated in 2004. New York Mayor Michael Bloomberg was an important supporter. The southernmost section reopened as a city park on June 8, 2009. The middle section is still being refurbished, while the northernmost section's future remains uncertain, access disputed between the City of New York and the MTA.
And here's the website of the High Line organizers: http://www.thehighline.org.