Some wild stuff happens in the belly of New York City's subway. Commuters flit back and forth, pushing each other out of the way, while trains roar into the station. Couples argue, babies cry aboard cars. Partygoers yell loudly, filled with jubilation at the prospect of the beginning of another evening. Performers play their instruments, singing loudly, hoping for spare change from generous tourists and New Yorkers.

But not many expect one of those performers to be famous-so naturally, many were shocked when they found jazz pop singer Michael Bublé belting out his song "Who's Lovin' You" at the West 67 Street stop in Manhattan.

Joined by group Naturally 7 as his backup singers, the Canadian crooner, dressed in a black, slim suit, snapped his fingers heartily while singing the new tune off his album "To Be Loved."

"That is the coolest thing ever, man. That is when you know you've made it, when you sing in the New York subway," Bublé said in an interview after his impromptu performance. "I feel like it's the most authentic, organic way to make music. You see the greatest musicians in the world perform down here."

He also mentioned that it was the most exciting thing he looked forward to in his travels to Europe, and elsewhere in the US.

Subway performers have long piqued interest in the general public-who are these enigmatic singers, dancers, musicians, that choose the bustling, muggy underground as their venue?

Blogger Michael Chin writes the stories of the subway performers he sees on his blog, Soundtrack Subterranea.

"[Subway performers] are too often overlooked because they blend in so well with the fabric of the city," Chin said. "It's a testament to their importance that even the ones without permits are still allowed to play."