New Yorkers don’t mind being underground when the surroundings are as welcoming as Rockefeller Center’s concourse or Grand Central Terminal’s Oyster Bar. But when James Ramsey and Dan Barasch announced plans for the Lowline in an abandoned trolley terminal below Manhattan’s Lower East Side, they set the underground bar even higher. That’s because they promised not just a shopping or dining destination, but a park with thousands of plants growing in Edenic profusion beneath Delancey Street.

That posed a technological challenge that Ramsey, a former NASA engineer, and Barasch, now the full-time director of the Lowline, have spent six years addressing. Their goal is to “concentrate” sunlight above ground, then send it through plastic tubes to underground diffusers that will simulate natural lighting well enough to keep plants photosynthesizing.