A whispering gallery is an area with a domed ceiling where two people can softly converse even though they are standing many feet (or meters) apart. The two most famous examples are found within St. Paul's Cathedral in London and Statuary Hall in the US Capitol.
There is also one located in the dining concourse in front of the entrance to the Oyster Bar in NYC's Grand Central Station. There is no sign marking the gallery or any instructions posted on how to make it work. However, by waiting a few moments, an in-the-know couple will walk up and show you the way.
If that doesn't happen, you and a partner need to stand in opposite corners below the tiled ceiling. You need to be facing very close to the corners, around 2 to 3 inches from it. Speak in a soft to normal tone and your friend should be able to hear you quite clearly, as if you were standing next to one another.
Over the years, Grand Central's Whispering Gallery has become a romantic spot for paramours wishing to quaintly exchange sweet nothings. It's also a popular scene for proposing marriage, especially around Valentine's Day, so be careful what you are getting yourself into.
If someone asks you how or why it works, try to recite some of the following explanation and use lots of the big words. A whispering gallery occurs beneath a domed ceiling constructed in the form of an ellipsoid with a parabolic dish at each focus (usually a corner). When someone faces one dish and whispers, the sound telegraphs from this focus until it reaches an opposite dish, where another person waits to receive the message.