The third intersection around the circle is P Street. Proceed to the right down P Street, where you'll immediately cross 18th Street, and simply proceed 2 more blocks to 16th Street. Turn right and the building is the second entrance at 1400 16th Street. See general location information above, as well. Directions for the subway and driving are provided below.
Cabs are also available, but they tend to be expensive.
Take the 395N exit to cross the river. While crossing the river, remain in the far left lanes, as there is a split just across the river. You'll want to take the left split. Now simply follow 14th Street about 15-20 blocks to P Street Northwest. Turn left on P Street and proceed 2 blocks to 16th Street.