The High Line

In 1847, the City of New York authorized street-level railroad tracks down Manhattan’s West Side. For safety, the railroads hired men – the "West Side Cowboys" – to ride horses and wave flags in front of the trains.Yet so many accidents occurred between freight trains and other traffic that 10th Avenue became known as "Death Avenue". After years of public debate about the hazard, in 1929 the city and the state of New York and the New York Central Railroad agreed on the West Side Improvement Project, which included the High Line. The 13-mile project eliminated 105 street-level railroad crossings and added 32 acres to Riverside Park.
The High Line opened to trains in 1934. It originally ran from 34th Street to St. John's Park Terminal, at Spring Street. It was designed to go through the center of blocks, rather than over the avenue, to avoid the drawbacks of elevated subways. It connected directly to factories and warehouses, allowing trains to roll right inside buildings. Milk, meat, produce, and raw and manufactured goods could be transported and unloaded without disturbing traffic on the streets. This also 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. The growth of interstate trucking in the 1950s led to a drop in rail traffic throughout the nation. The last train was operated by Conrail in 1980 with three carloads of frozen turkeys. In the mid-1980s, a group of property owners with land under the line lobbied for the demolition of the entire structure. Peter Obletz, a Chelsea resident, activist, and railroad enthusiast, challenged the demolition efforts in court and tried to re-establish rail service on the Line. In the 1990s, as the line lay unused and in disrepair – although the riveted steel elevated structure was basically sound – it became known to a few urban explorers and local residents for the tough, drought-tolerant wild grasses, shrubs, and rugged trees such as sumac that had sprung up in the gravel along the abandoned railway. It was slated for demolition under the administration of New York Mayor Rudy Giuliani.
A non profit organisation saved the line from demolition and then spent the next few years turning the structure into a public park. The success of the High Line in New York City has inspired other cities to investigate the feasibility of replicating it in their cities, "including Chicago, Philadelphia, and St. Louis..." It costs substantially less to redevelop an abandoned urban rail line into a linear park, rather than to demolish it.
Apart from all that it is a great place to go visit if you are NYC. Just saying.