Visiting the two Brooklyn Parks and learning of many parks around the city reminded me of a proposed underground park for the East side of Manhattan titled the Lowline.
The idea of the park was born out of an interest in re-appropriating public space, specifically the abandoned Williamsburg Bridge Trolley Terminal spanning 1 acre underground. The architecture firm Raad Studio began designing technology to make sun light available below ground. In the last few years they have created and exhibited these designs in the Lower East Side. Within the next couple of years the firm aims to negotiate with the MTA and city to build the Lowline.
The New Yorker wrote an article about the proposed park- http://www.newyorker.com/culture/culture-desk/meet-the-lowline
The Lowline website also provides more visuals and information about the project- http://www.thelowline.org/about/project/