Steve Duncan lives dangerously. The urban explorer goes underground, examining the hidden infrastructure of major cities all over the world — their tunnels, subways, sewers.

In New York City, his favorite underground adventure, he could drown when the tide comes in or succumb to toxic gases in the sewers. He could be hit by a train or step on the third rail. And if he gets caught, he would be so under arrest.

So why does he do it? Read more of National Public Radio’s article after the jump to find out!