After a fantastic trip to England and Morocco this weekend, today I headed back to New York. Whenever I’m back home in the U.K., it never feels long enough and I have to tear myself away. But the minute I land and see that skyline, I realize exactly why I came back.

It was late when I got home so I only fancied something quick. I headed north to get my fix at Grand Central Station. Yes, I sought out another of its secrets.

When you arrive at the Main Concourse, it’s easy to be wooed by its glorious size and grand decor – and sometimes hard to remember to look up. Yet if you look above, you see a gorgeous sky painted with constellations.

Now, go to the west side of the roof and look up near to Cancer, the crab. See it?

Follow the line of the zodiac to the wall and do you see anything? A little dark patch where the green meets the cream?

This dark brick is a nod to what the station’s ceiling used to look like before it was cleaned in a massive MTA restoration project in 1988. Disgusting eh? The concourse is so beautifully manicured and well lit now, that I can’t imagine how dark, dingy and dirty it would have been back then.

You might think the dark patch came from soot from the trains, but after teams carried out research following the clean-up, they learned it’s actually mostly nicotine and tar – and therefore the result of the cigarette smoke that used to swirl inside the terminal.

Now it’s here as a reminder of how the terminal used to be before the restoration. So it also serves as a reminder of how grand and tidy it is today. (Plus, it’s a pretty good anti-smoking ad.)

This is another little gem in Grand Central and definitely one of those things you wouldn’t even notice if you checked out the ceiling without knowing about it. So if you’re there, don’t forget to look up and appreciate that gorgeous clean ceiling.