How did North Korean soldiers wander across the world's most heavily guarded border?
Don’t believe the name: The Demilitarized Zone between the two rival Koreas might be the most heavily armed place on earth. Two million mines, barbed wire fences, tank traps and tens of thousands of troops from both countries patrol a divided swath of land 248 kilometers (154 miles) long and 4 kilometers (2.5 miles) wide.