On Thursday, July 14, New York’s City Hall officially gave the Lowline—a proposed underground park, built inside an abandoned trolley terminal on Manhattan’s Lower East Side—the green light, New York magazine reports. The park still has a long way to go before it officially becomes a reality, but its developers are now one step closer to their goal of building the world’s first subterranean natural attraction.

The Lowline’s creators, James Ramsey and Daniel Barasch, have spent the past eight months bidding to become the one-acre trolley terminal’s appointed developers. No one else submitted a proposal to use the space, DNAInfo points out, which made it easier to win over the city’s Economic Development Corporation. Their idea intrigued officials, who say they’re excited to see how the Lowline’s special solar-harnessing technology will transform the empty public transit hub into an oasis of plants and flowers.

“The Lowline represents an incredible fusion of technology and public space. For eighty years, this underground space has sat idle. ... We can’t wait to see this experiment unfold,” Alicia Glen, New York’s deputy mayor for housing and economic development, said in an announcement quoted by the New York Daily News.

But even though the Lowline just cleared a major developmental hurdle, Ramsey and Barasch still have to meet certain fundraising and development criteria if they’re going to keep the space. For example, they have to prove to the city that their light-harnessing tech—which uses fiberoptic cables and mirrors to carry sunlight underground—can actually keep an acre of plants alive underground all year long. From last October through March 2016, a preview space called the “Lowline Lab,” installed inside a warehouse a few blocks away from the Lower East Side trolley station, provided the public with a temporary simulation of how the project works. 

The Lowline concept is also extremely expensive: It will cost a cool $60 million alone to build, and it might require maintenance fees of as much as $4 million per year. So far, New York City hasn’t promised any money toward the Lowline, although they’re not dismissing the idea of using public funds just yet. Ramsey and Barasch have to raise $10 million in 12 months, brainstorm a design scheme, and receive public feedback at community meetings. And that’s not even taking into account that the terminal has to be rezoned, thanks to the city’s uniform land-use review process

Looking at the popularity of New York’s High Line—an aboveground public park that’s built across an old freight rail line in Manhattan—it seems like a no-brainer that many people would also love the Lowline. But not everyone’s pleased with the proposed project, claiming that it will hike up local rents and draw too many tourists to an already-crowded neighborhood. Some people are also upset that the city didn’t allow more time for people to submit additional proposals to re-make the terminal. And until Ramsey proved that only two buses could fit inside the abandoned terminal, transit workers were wondering if they could transform the space into a modern bus terminal.

But at the end of the day, both Lowline supporters and the project's naysayers have to sit tight and wait: Even if the Lowline ends up meeting all city criteria, it still won’t be opening until at least 2021. 

[h/t New York magazine]