Q. What is the address of the Library?
We generally use "37th and O" as the Library's address when giving directions, but a fairly close approximation is "3700 O Street NW." Both these locations will bring you to the GU main gate; the Library is on the left (south) edge of the Healy Lawn as you pass through the gate.
You could also use latitude/longitude of Healy Hall (N 38° 54.412 W 077° 04.368), which is the closest benchmark to the Library.