Despite my earlier fears, it appears that my memory banks are still a treasure trove of semi-useless information. The mystery photo is indeed the waiting room at New York's old Grand Central Station, constructed in 1898 when the original depot was enlarged.
The photo is from the Library of Congress, and appears in Belle & Leighton's book, 'Grand Central: Gateway to a Million Lives.' In the book, the image has a higher resolution, so you can see the names of various destination cities (Albany, Troy, etc.) carved into the frieze above the arched windows.
This appears to be the waiting room for "respectable" passengers. The railroad maintained a separate waiting room for "immigrants." Like many magnificent public spaces in New York during that period, it had an extremely short life span. It existed for barely 12 years before it was demolished, in 1910, to make way for the current Grand Central Terminal.