Producers apparently had the typically-busy train station cleared out for the pre-taped set, during which the "Boy with Luv" hitmakers belted out their new single, "ON", complete with a group of dancers and a marching band.
It's not clear when the seven-piece group stopped by the landmark, but prior to the Monday night (February 24) broadcast, show host Jimmy Fallon explained, "We wanted to do something special for BTS and, at the same time, celebrate New York City."
"BTS really knocked it out of the park. You're not going to believe how big and fun their performance is. They took over Grand Central Terminal."
The unique gig came at the end of a mini tour of the Big Apple, with Fallon taking the South Korean stars to eat at the iconic Katz's Deli, before jumping on the New York City Subway public transportation system to play a series of games and answer fan questions about their new music.
"He's a big fan of us. It's mutual, of course," he shared. "We were always watching WWE when we were like, 13."
The revelation prompted Fallon to promise an introduction to the "Trainwreck" star. "I'm going to get you hooked up with John Cena," he declared.