The most recent exodus of North Korean defectors into China began in the late 1990s after a severe famine that killed at least one million of its 23 million people. Most follow an escape route known as Asia's Underground Railroad, eventually covering more than 10,000 km if they successfully reach Seoul. Their first step is to cross the border at the Tumen River. They then remain in hiding, waiting to escape from China. The 2,000 perilous miles across China are just the beginning. Then comes the challenge of making a new life.