Verdant oases have been squeezed into every corner of New York City, tucked between towering skyscrapers, carved from former military posts and abandoned railroad tracks, and even laid on top of landfills.

But it is still not enough. So now the latest frontier in the quest to carve out more parkland is the city’s subterranean level — home to subways, sewage lines and rats.

Plans are underway to build what its supporters say would be the world’s first underground park.

An abandoned trolley terminal near the Williamsburg Bridge on the Lower East Side of Manhattan would be transformed into a green space built by a nonprofit group that has spent years experimenting with solar technology. The group proposes to illuminate the underground space with sunlight collected by high-tech panels above ground and reflected down through a series of pipes.