As North America's largest metropolis and one of the most iconic cities in the world, New York City is often seen as an extraordinary open-air urban lab by city enthusiasts. The High Line—an elevated railway converted into a park and designed by Diller Scofidio + Renfro—has made headlines around the world and is often cited as a successful example of urban renewal and adaptive reuse. Today, six years after the first section of the High Line opened, several cities around the globe are creating their own version of the famous elevated park.

The High Line in New York City, image by Flickr use David Berkowitz

The first section of New York's High Line opened to the public as a park in 2009, but its history goes back to 1934, when the elevated railway first opened to trains carrying goods through Manhattan's most industrial district. In 1980, after a steep decline in rail usage, the railway eventually closed and fell into a state of disrepair. After several attempts from neighbouring property owners to demolish it, the fate of the High Line got brighter in 1999, when locals created the Friends of the High Line Association in an attempt to advocate for its preservation and reuse as a public space. In 2014, the third and northernmost section of the High line opened to the public, forming a 2.3-kilometre linear park that attracts more than 5 million visitors annually.

Coulée verte René-Dumont in Paris, image by Jean-Louis Zimmermann via Wikimedia Commons

This high-profile park is not the first initiative of its kind. Inaugurated in Paris in 1993, the Coulée verte René-Dumont—French for green course—was the first green space to be constructed on elevated infrastructure. Running above the streets and cutting through city blocks over a distance of 4.7 kilometres, the green course is supported by the disused Vincennes railway line. While some parts are up to 10 metres above ground, some parts go through sections situated below street level in a mix of enclosed and open air trenches, giving visitors a break from the busy streets above.

Sydney's Goods Line, image courtesy of the Sydney Harbour Foreshore Authority

On the other side of the planet, Sydney is also building a public space atop a former railway. The project, known as the Goods Line, will eventually span over 500 metres in length, connecting the Ultimo neighbourhood to the rapidly developing Darling Harbour, which was once one of the most lucrative harbours in the British Empire and connected to a nearby yard by rail in 1855. Today owned by the Sydney Harbour Foreshore Authority, the first section of this repurposed railway opened to the public last August, providing new recreation spaces for more than 80,000 students and locals.

Seoul Skygarden, image courtesy of MVRDV

In Seoul, it is a former highway that Dutch architects from MVRDV will transform into an elevated garden. Located near Seoul's busy Central Station, the 938-metre long, 17-metre high structure will soon become a lush ribbon populated by 254 species of trees and other plants. Appropriately named the Seoul Skygarden, but also refered to as the Plant Library, it will catalogue local flora in alphabetical order and cover a total area of 9,661 square metres. While cafes and restaurants will generate revenue for the city to cover the costs of renovation and maintenance, the Skygarden will provide pedestrians with a new passage over the station that is 15 minutes faster than the current at-grade walk, and support the city's effort to become a more pedestrian-oriented and environmentally-friendly place.

The Transbay Transit Center, image courtesy of Pelli Clark Pelli

In other cities, smaller structures also aim to add elevated green spaces to the busy urban environment. In San Francisco, the construction of the new Transbay Transit Center will include a 5.4-acre, 430-metre long park on the roof of the bus and rail station. This is a welcomed addition to a neighbourhood that has strong projected growth, with 560,000 square metres of office space, over 4,000 units of new housing and 1,000 new hotel rooms. Finally, London is planning to construct a 366-metre pedestrian Garden Bridge that will stretch across the River Thames from the top of Temple underground station on the North bank to the South Bank, although recent controversy has put the future of this project in doubt.

London's Garden Bridge, image courtesy of Heatherwick Studios

While elevated green spaces have been encouraged by the success of New York City's High Line, a new kind a public park hopes to see the light of day in the Big Apple: the underground Lowline. Nestled within the one-acre former Williamsburg Bridge Trolley Terminal below Delancey Street on the Lower East Side of Manhattan, the park will use remote skylight solar technology to illuminate the space and enable trees and plants to grow. Designer James Ramsey of Raad Studio explains that "in this approach, sunlight passes through a glass shield above the parabolic collector, and is reflected and gathered at one focal point, and directed underground. Sunlight is transmitted onto a reflective surface on the distributor dish underground, transmitting that sunlight into the space."

Demo of the Lowline, image by mike via Wikimedia Commons

Expected to open in 2020 after a fundraising campaign for its construction, the Lowline will be operated by the City. Currently visitors can head to the Lowline Lab to see experiments in underground horticulture as well as a sample of the remote skylight technology. Thanks to this new technology and the growing popularity of adaptive reuse projects, the potential for dense cities to create additional and unusually located green spaces are immense and should develop further in the upcoming years. In the meantime, you can tell us about your favourite adapted parks by leaving a comment at the bottom of this page or in the Forum's corresponding City Threads.