Asia's Underground Railroad

[Image: Barbed wire marks the high-security zone where the frontiers of Russia, China, and North Korea meet at the Tumen River. This river is where most North Koreans sneak into South Korea during the summer, when the river is shallow enough to wade, or in winter, when it's possible to walk across the ice. National Geographic (Text: Tom O'Neill, Photographs: Chien-Chi Chang), Feb. 2009.]

A great feature in this month's National Geographic on the Asian underground railroad that refugees from North Korea continue to use at great risk to reach Thailand, where they have the best chance of finding a new livelihood since, unlike many of the region's nations, Thailand does not practice a policy of returning North Korean "illegal immigrants" back to their homeland.
Back in the nineties when North Korea was plagued by famine the migration route mostly passed though Southern China, but the Chinese have since increased border controls there, which have relocated paths through Mongolia. However, it wasn't long before the Mongolians established their own security barriers and pushed migrants further out into the hard traveled Gobi desert. Eventually, the exodus geographies began to extend into Mynammar, but the dangerous militarized zones there have highly discouraged this option from becoming too well tread. After getting through China, Vietnam used to be an option, but in 2004 the government dramatically clamped down on the informal border crossings there and send refugees back to Korea.
Today, the most commonly used escape route has been diverted through South Korea, China, over the mountain ranges of Loas, and then into Thailand. I have come across some good coverage recently, but will leave you to read through the articles on your own. I will just drop this quote from the National Geographic piece for now as a point of departure:

Some 50,000 North Koreans, and possibly many more, are hiding in China, most in cities and villages along the remote 900-mile-long border between the two countries. Uncounted others have come for a few months and then slipped back to North Korea with food and money. Yet many stay on, unable or unwilling to return to their cruel homeland. They are left with two desperate choices: Keep hiding—often as prisoners of exploitative employers—or embark on the Asian underground railroad, a perilous journey by foot, vehicle, and train across China and Southeast Asia. Confronted with an obstacle course of checkpoints, informants, and treacherous terrain, numerous defec­tors have been caught. But aided by a small band of humanitarians and by smugglers charging $3,000 and up, some 15,000 have reached safe haven, most often in South Korea. There, traumatized and barely skilled, they face the most formidable challenge of all: starting over.

Further reading:

North Korea's underground railroad to Thailand
Get my drift, Dear Nation?
An 'underground railway' rolling to freedom or death Missionaries play dual role in lives of Korean refugees