The Bridge of No Return crosses the Sacheon River, which forms part of the border between North Korea and South Korea, in the town of Panmunjom. It's about two car lanes wide, but there are barricades on either end so that you can't drive on it.

When the Korean War ended in 1953, POW's on both sides were given the choice to go back home or stay, and those who wanted to go back did so by crossing the Bridge. They couldn't return once they crossed the bridge: hence the name.

Later, in 1968, a group of captured American sailors from the USS Pueblo crossed the Bridge of No Return, one at a time, to return to the free world side of Korea.

Since those two occasions, nobody has ever crossed the bridge (aside from James Bond in Die Another Day). Both sides have military patrols on their respective ends, and even if you got past them, they would probably shoot you. Again, hence the name.