The garden is located on Fourth Avenue in Park Slope, between Sackett Street and Union Street. The street address is 207 Fourth Avenue, Brooklyn, 11217.
The garden is on NYC Department of Environmental Protection (DEP) land known as Watershaft 22B, one of many watershafts connected to the Third Water Tunnel. Find out more here: http://www.water-technology.net/projects/new-york-tunnel-3/
http://www.nyc.gov/html/dep/html/drinking_water/wsmaps_wide.shtml