Since the inception of The High Line, the New York park perched on a once-abandoned railway track, cities around the world have been reclaiming unused infrastructure to create new pockets of green. Now, the trend is headed underground with the Lowline, a proposed park that could occupy a disused trolley terminal under the streets of Manhattan.

The project is the brainchild of Dan Barasch and James Ramsey, who have spent the past eight years developing the proposal and introducing the concept to the public through their Lowline Lab, where they've been testing the "remote skylight" technology that brings light to the project. Just this week, their proposal got its first city approval, a major step towards making the park a reality.

"Every designer dreams of doing civic work that contributes to society and to the profession." —Lowline creator James Ramsey

From here, the developers will need to raise $10 million in a capital campaign and present new plans to the city for approval. The one-acre park would occupy a former trolley terminal that has stood unused since 1948. If approved, it could open as soon as 2021.

The project is about more than just creating an underground park. The hope is one day the technology will be able to be used to capture and utilize natural sunlight in other applications, including at offices, hospitals, schools, and even prisons.

See more from our visit to the Lowline Lab here.