The hundreds of North Korean refugees who have arrived in the South from Vietnam this week will have had a long and frightening journey.
By Sarah Buckley
BBC News Online
For many, that journey is likely to have started at the Tumen River, which separates North Korea from China.
North Korea's river border is shallow enough to wade across in summer
This narrow waterway can be walked across in winter, when it freezes over, and waded across in summer.
But South Korean activist Kim Sang-hun told BBC News Online that the crossing was very risky.
"It's heavily guarded on both sides," he said. "There are some people who went to the top of a hill nearby and watched the guards for days, and picked the right time."
Others risk bribing the guards with cash, drink or cigarettes.
Once across the river, escaping North Koreans are unlikely to spend much time on the heavily-patrolled border, said Kato Hiroshi, head of a Japanese NGO which helps North Korean refugees.
Instead, they make their way into the mountains, and from there into populated areas to find work. This alone might take five to seven days, depending on the refugee's connections.
They also need to change their clothes to make themselves less visible.
Many initially settle in the three northern provinces of Jilin, Liaoning, and Heilongjiang, where they are sheltered by one of many underground Korean networks in northern China - an area which is highly populated by ethnic Koreans.
They seek work - perhaps in mines, factories or cattle farms - but are often swindled out of their earnings.
A mine owner might promise them 500 yuan a month, but actually they are paid less than half, or nothing at all - forced into acquiescence by the fear of being reported to the authorities.
Those who then choose to leave China - like the 450 or so who arrived in Seoul this week - use their earnings to begin the long dangerous journey across the vast landmass.
For someone who is totally free to travel, it only takes about three days to reach China's southern border by train.
But Mr Kato said long-distance trains were frequently boarded by railway police who check passengers' identity cards, so North Korean refugees usually make shorter train journeys of up to three hours at a time.
If they make it to China's southern border, North Korean refugees face another nail-biting crossing.
This is done either under their own steam, with the help of humanitarian aid workers, or through commercial brokers who charge about $2,000-10,000 per person, according to Mr Kim.
Many will fail at this point. According to Mr Kato, China has substantially strengthened its border patrols in a bid to stem the stream of fleeing North Koreans.
Under a treaty with Pyongyang, Beijing is obliged to return them to North Korea.
Those that make it into one of the countries of South East Asia are for the most part looked after by Korean societies, including the Christian church, who give them shelter, food and clothing, said Mr Kato.
They must then play a waiting game.
Mr Kato said that ideally they should make their way to the UN refugee agency's office to register their refugee status. The UNHCR will then make contact with the South Korean embassy to arrange passage to Seoul.
"They wait their turn - sometimes it takes one year," he said.
But not everyone manages to be so patient, he added.
"In Thailand, in Vietnam, in Cambodia, each government allows to let them stay [without papers], but people can't wait so long, they have already had a very hard time in China," said Mr Kato.
These people will attempt to storm the South Korean embassy, a headline-grabbing incident which Mr Kato said was diplomatically embarrassing for all countries involved.
"They need to transport them silently," he said.
But this face-saving method has become unsustainable in Vietnam.
"Because the number [of North Koreans] has come to be so big, the limit is over to keep silent. Every concerned country cannot close their eyes - there are so many," he said.
Chinese official media says 8,000 North Koreans cross into China every year - but activists estimate the number at more than 10,000.
Kim Sang-hun estimates that most refugees are sent back at least once
The 450 North Koreans who have just arrived in Seoul are the lucky ones. Mr Kim estimates that 70% of refugees fail at some point in their journey.
"Of the defectors who have safely arrived in South Korea, you rarely find refugees who have never been arrested," he said.
Failure can mean incarceration in North Korean prisons or concentration camps, or even execution - sometimes extra-judicially.
But, he said, "a number are released after two to six months because they keep denying [that] while they were in China they were ever in contact with South Koreans."
Many of these will try again to leave the country at a later stage, he added.
It is not every North Korean's goal, however, to reach the promised land of the South.
"Many of them would prefer to stay in China," said Mr Kim.
"They are [then] very close to their home country. China is already good enough for them in terms of food and everything, and they hope that their government will collapse soon."
In addition, "if they are in China, they are only officially termed as missing in North Korea, in which case no family or relatives will be punished."
Mr Kim said most refugees were underfed, but that was not what was primarily motivating them.
"I often meet defectors who say 'I didn't come here because I was hungry. I wanted to live as a human being.'"