NewYorkology: A New York Travel Guide:
Among the secrets of the Grand Central Terminal is the "whispering gallery" in front of the famous Oyster Bar & Restaurant. There is no sign marking the gallery or how to make it work. But if you wait a few minutes, a couple will undoubtedly walk up and head to separate corners and elicit its magic.
The low ceramic arches, built for the 1913 opening of Grand Central, are designed in such a perfect way that if two people stand at diagonal arches and whisper into a corner, they should be able to hear each other as if they were face to face – not far across the way.
"I was raised in New York and my father taught me about it when I was just a little, little girl," said Catherine Wiley, who was visiting recently from Brookings, Ore. On this trip, she was traveling with her boyfriend, Ed McDonald, and she brought him to Grand Central to show him the trick.