A moving train.
The country star, who released his new album, Get Closer on Tuesday, joined forces with Amtrak to stage two surprise performances at New York Penn Station and Philadelphia's 30th Street Station, and then put on an acoustic show for 50 contest winners aboard the train itself.
"I've never performed on a train," Urban told PEOPLE. "I'm not even sure how I'll be able to stand!"
His day began in midtown Manhattan. "I finally made it to Penn Station – to heck with Madison Square Garden," he joked to the crowd. "I can check this off my bucket list now."
After playing a handful of old hits and new singles, Urban teased, "I want to thank you all for missing your train today."
The New Yorkers weren't the only ones to skip the train for a show. A massive crowd in Philadelphia greeted the singer and sang along with six of his hits.
"Things like this don't seem to happen much around here," Colleen Hansen, 24, told PEOPLE. And while she's been to an Urban concert, the train station show proved to be a bit more intimate. "I just texted my friend, I'm about to be five feet away from Keith Urban!"
And despite his concerns about taking a tumble aboard the train back to New York City, Urban's railroad show went off without a hitch.
"We are playing on a train! That's awesome," he said, safely perched on a seat with his guitar. Well, almost without a hitch. "We're trying to use the dang drum machine on the train and its not working" he joked of the malfunctioning equipment.
And as the train rolled through New Jersey toward the city, he concluded his hit "Raining On Sunday" with some new lyrics. "I can't believe," he sang, "I haven't fallen once yet!"