The Goddard Institute for Space Studies is located in New York City at the northeast corner of the intersection of Broadway and West 112th St., in the Columbia University / Morningside Heights neighborhood of Manhattan. Right at the corner on the first floor is Tom's Restaurant, a restaurant which you will likely recognize if you have ever watched the TV program Seinfeld.
Their front entrance is just a few steps east along 112th St. from Tom's. Immediately above the entrance is a sign stating 545 West 112th St. There is a smaller sign to the side stating 2880 Broadway, their official address.
Here is a map to The Goddard Institute for Space Studies.
GISS is a small research installation, and as such does not provide for drop-in visitors. Tours are available only on an extremely limited basis. Contact Ms. Emily Michaud at emichaud@giss.nasa.gov or 212-678-5641 for further details.