It’s not easy for a K-Pop group as big as BTS to set foot in a public space without people noticing them—much more in a crowded place like the Grand Central Terminal in New York City.

Surprisingly, the boys pulled it off.

As part of a series of promotional shows in the U.S., BTS made an appearance on Jimmy Fallon and agreed to do a number of segments such as an interview inside a moving subway train and another where they sold food at a popular sandwich store.

The #FallonAsksBTS segment, which was a Q&A with questions gathered from BTS ARMYs online, apparently took eight hours to film.

But what’s more noteworthy is the fact that the K-Pop icons managed to perform inside the Grand Central Terminal Station without anyone seeing them. So how exactly did they pull it off?

The President of the MTA Metro-North Railroad Catherine Rinaldi, in an interview with The New York Times, revealed it took two months of making painstaking arrangements to make the whole thing happen.

“It’s Saturday so it’s a much quieter time. We are over the moon about how successful this has been,” Rinaldi said.

Shot on a Saturday, the entire production crew, as well as the backup performers, had to start setting up at the venue at 10 in the evening.

At around 12 midnight, BTS, composed of members M, Jin, SUGA, J-hope, Jimin, V, and Jungkook arrived at the station.

Then, at 2 A.M., the cameras started rolling for their performance of the song “ON” which is part of their latest album Map of the Soul: 7.

But since the terminal was expected to open its doors to the public at 5:15 A.M., they were only given two hours to shoot the entire performance.

Watch the video below:

While opting not to disclose the payment made by Fallon to make the video, she, however, revealed that there is a corresponding fee for shoots made inside subway stations.

Various Hollywood films and music videos have been shot inside the Grand Central Station in the past.