With the rising ocean waters (fact), hurricanes that hit New York City (fact), and overall bad weather that rains so much that parts of NYC floods (fact)… Building an underground park is rather ludicrous!
Elevation Map of Mathattan, NY: http://en-us.topographic-map.com/places/Manhattan-554568/
You’ll see the elevation around the Williamsburg Bridge is between 6 feet to 10 feet high. And you build an underground park which means you are now -2 feet to 0 feet above sea level. Add that to all the natural disasters that hit NYC… Brilliant!
TQQdles™