You See Rubble and Garbage. She Sees New York’s Next Great Park.

The area under the Brooklyn Bridge in Lower Manhattan is a forbidding swath of rubble and construction equipment, cut off from the sky by six lanes of clattering bridge traffic. To most of the world, it communicates a single message: keep out.

To Rosa Chang, it conveyed something different: New York City’s next great park.

On a walk around the site last month, Ms. Chang peered through a chain-link fence at a few pieces of idle heavy machinery and described what she saw. She wore a bright red dress and high-wedge sneakers and the beatific smile of a true believer.

“I see opera,” she said. “I see children playing, I see trees, I see old people sitting down talking to each other. I see skateboarders flying in the air, I see nature, I see one of our most beautiful structures that humanity has ever been able to build anchoring it all.” In the sealed brick vaults under the bridge, which long ago housed a vast wine cellar, she saw a public library and a maker lab and museum. She saw an outdoor swimming pool.

“Go on, tell me the truth,” she said. “Do you think I’m crazy? Or do you think this is common sense?”

For the last three years, Ms. Chang has led such walking tours of the site for city officials, community leaders and potential allies, pitching her vision for what she calls Gotham Park, along with her project’s estimated costs: $200 million in public and private money.

“Her strategy is to kill with kindness,” said Mark Levine, the Manhattan borough president, who became an early supporter after a walking tour with Ms. Chang. “She radiates positivity, but she is relentless. I mean this in the best way, but she always has an ask. You never get out of any conversation without an ask.”