It takes barely an hour to drive from downtown Seoul to the other side of the demilitarized zone, but the culture shock is such that you might as well be commuting to the moon.
Mobile telephones, newspapers, books, videos, laptops, magazines, MP3 players and many other appurtenances of 21st century life have to be checked on the south side of the border.
Also best left behind are any wisecracks about the North Korean regime, in particular those involving its leader, Kim Jong Il.
"You've got to watch what you say," said Kim Yi Gyeom, a South Korean telecommunications worker standing in a long line of Monday morning commuters waiting to go north. "The spirit of openness has not come to North Korea yet."
In the boldest experiment in inter-Korean cooperation to date, nearly 500 South Koreans are working side by side with more than 6,000 North Koreans in a year-old industrial park just north of the DMZ.
South Korea is assuming all the financial risk, having invested more than $2 billion.
The South would like to reduce political tensions and reap the benefit of cheap North Korean labor so its manufacturers can compete with China.
For the North Koreans, the experiment is a way to build their economy with only the most limited dose of openness to the outside world. But the North is also bearing all the political risk: Contact with the better-fed, better-clothed South Koreans could endanger the government's grip on power.
"It is natural that there is a culture gap," said Hwang Boo Gi, director of the Kaesong Industrial District, who led a group of foreign journalists through the park Monday. "We are talking about the difference between capitalism and socialism."
Or as a North Korean official, Han Cheol, said diplomatically, "We like to emphasize what we have in common, like our heritage, and not our differences."
Nevertheless, the contrast is particularly glaring when coming from Seoul, the high-tech, neon-lighted capital of the world's 12th-largest economy. Around the industrial park, which lies outside the center of the city of Kaesong, there is little but desiccated rice paddies and yellow hills denuded long ago by people scavenging for firewood. Nearby is an abandoned agricultural college, its crumbling facade decorated with a faded red sign trumpeting the achievements of the North Korean Workers Party. Scrawny goats graze outside two-story whitewashed houses with windows covered in plastic sheeting.
The industrial park itself is surrounded by 5 miles of fencing and poker-faced, rifle-toting North Korean soldiers.
Inside the compound everything from the toilets to the machinery is South Korean-made, mostly the state-of-the-art model.
Although all 11 companies now operating in the 23-acre pilot project are South Korean, the North Koreans keep a tight rein on the work environment. No South Korean money is accepted here, even at a Family Mart convenience store set up for the exclusive use of South Korean employees.
North Korean patriotic music in praise of Kim blares over the loudspeakers of a futuristic warehouse where North Korean women in crisp blue uniforms stitch athletic shoes using brand-new sewing machines.
The monthly salaries of $57.50 for each North Korean worker -- regardless of position -- are paid directly to the North Korean government, which in turn gives the workers about $8, more than double the average monthly salary. South Korean companies have asked repeatedly to pay the workers directly and to give bonuses for better work, but have been refused.
Even New Year's gifts such as extra food and warm clothing could be given only after elaborate negotiations to make sure everybody was getting the same.
South Koreans, many of whom live for weeks at a time in modular housing in the complex, have their own cafeteria and their own medical clinic, all off limits to the North Koreans.
Last year, articles appeared in the South Korean press about a purported Romeo and Juliet romance between a North Korean woman and a South Korean man. But people at Kaesong said the story was apocryphal because the North Korean women are never alone.
"They even go to the toilets in pairs," said a South Korean employee who asked not to be quoted by name. "There are big social differences between us. There is no sense of the individual in North Korea."
There have been countless cases of culture shock.
When Shinwon, a garment company located in the complex, held a fashion show in October -- complete with disco music, strobe lighting and slinky models in denim miniskirts -- it offended the conservative sensibilities of some North Koreans.
For their part, some South Koreans were taken aback recently to see North Korean workers dancing and singing enthusiastically to accordion music at a fuel pump factory. It turned out they were rehearsing in anticipation of Kim's birthday Feb. 16.
"It was a contest of who could best show their loyalty to Kim Jong Il," said a South Korean worker who asked not to be quoted by name.
As is often the case, many misunderstandings have resulted from acts of kindness.
South Koreans have covertly tried to give medicine from their private clinic to ailing North Koreans.
One South Korean employee was accused of trying to bribe a North Korean soldier when he gave him two packages of instant ramen noodles, said a military source who requested anonymity.
In a more serious incident, a South Korean was caught trying to distribute Christian literature, which is strictly forbidden in the communist country, the source said.
"Almost every day something happens, some small quarrel or misunderstanding. But because Kaesong is so important to Kim Jong Il, the North Koreans chose to ignore it," said Lim Eul Chul, a scholar at South Korea's Kyungnam University who has written extensively on Kaesong. "Everybody is focused on the goal."
Both sides have ambitious plans for Kaesong. When completed in 2012, the enclave is expected to encompass 25 square miles and employ 700,000 people.
The biggest impediment to the project's success might be North Korea's nuclear weapons program and its hostility to the United States. The tensions have limited the nature of the products manufactured at Kaesong to low technology -- with anything having potential dual use for military purposes prohibited -- and mostly confined sales to the domestic South Korean market.
Although Shinwon Apparel, for example, supplies clothing to Kmart and Wal-Mart, among others, those garments are largely produced in Vietnam. U.S. officials, who this month announced negotiations toward a free-trade pact with South Korea, have said they would not consider Kaesong products to be labeled "Made in South Korea."
If the North Koreans are merely tolerating the presence of the South Koreans for their money, they go to pains not to show it. The well-disciplined North Korean cadres who were showing foreign reporters around Kaesong on Monday all lavishly praised their South Korean counterparts.
A young North Korean woman in a bright red dress and red heels, shivering in the February chill as she led the tour, smiled graciously as she delivered stock responses.
"Of course, it is a privilege for us to work with the South Koreans," said the woman, Kim Hyo Jeong, 25.