Discovering secret spots right and left! This one isn't really much of a secret, since they take point it out on all of the tours that swing by this nook of Grand Central. But it's impressive, nonetheless!
A whispering gallery is created any time a circular wall (most often under a dome) allows for softly uttered words to travel in waves along the wall to another individual standing well away from the original whisperer. There is one of these such walls in Grand Central Station, where a set of archways just outside the Oyster Bar form a miraculous 4-corner secret-telling spot.
If you stand at one of the corners of the gallery and whisper into it, your message will travel up along the dome and reach your partner-in-crime waiting at the opposite corner perfectly clearly. It's super weird. But very cool!
Apparently, this is quite a popular spot for marriage proposals (awwww).
Side note: I'm determined to hit every single item on THIS list. Keep you posted!!