New York Times
3 July 2012
By CHOE SANG-HUN
HWASEONG, South Korea - [...] Mr. Kim, 47, is one of a small but dedicated band of South Koreans who have been hunting for North Korean "invasion tunnels" for years, some for decades. Only four tunnels have ever been detected, all between 1974 and 1990 and all near the border. Not one has been found since, despite thousands of drilling operations conducted not only by the South Korean military but also freelance prospectors like Mr. Kim.
Although broadly dismissed as cranks, the private tunnel hunters tap into the source of one of South Koreans' greatest fears about North Korea: its penchant for taking its war preparations underground, a reaction to the leveling of its military installations by United States air power during the 1950-53 Korean War. [...]