Grand Central Terminal

The main concourse ceiling is a 1913 painted sky with the zodiac constellations picked out in gold — and it is reversed, shown as if seen from outside the celestial sphere looking in.

The official explanation is that it's a medieval convention. The other explanation is that the artist worked from a manuscript and got it wrong. Nobody has ever settled it.

There's also a small dark rectangle left unrestored near Michael the Archangel, deliberately kept to show what decades of tobacco tar had done to the whole thing before the 1990s cleaning.

Outside the Oyster Bar on the dining level, four ramps meet under a Guastavino tiled vault. Stand facing into a corner, have someone stand in the diagonally opposite corner, and speak quietly into the wall — they hear you perfectly, thirty feet away, across a crowded corridor.

It is free, it works every time, and most people walking past have no idea.

• The information booth clock in the middle of the concourse — four opal faces, and by a distance the most-used meeting point in New York.
• Vanderbilt Hall, the former main waiting room, now used for events and markets.
• The dining concourse below, with a proper range of food, and the Oyster Bar under the vaults since 1913.
• The acorn and oak leaf motif everywhere, the Vanderbilt family emblem, once you start looking.

It is called a terminal, not a station — every track ends here. Locals will not correct you, but now you know.