The other side was a different picture. A brand-new floodlit customs complex built by Hyundai, the cruises' organisers. As we disembarked, with the military-style buildings, the guards watching, the scurrying uniformed construction workers, it felt like arriving at the villain's secret base in a James Bond film.

Kim Jong-il: Film fan

I kept thinking about films when I was in North Korea. Perhaps that's appropiate. It's a land of fantasy, a worker's paradise with its own peculiar paranoid Korean form of communism, called juche which stresses self-reliance.

Its leader is Kim Jong-il, who must be the first leader of a communist country to inherit power from his father - the newspapers tell of rainbows appearing when he appears.

Kim Jong-il loves films. He likes them so much that in the 80s he got his secret agents to kidnap one of South Korea's leading actresses and her director husband to try to teach North Koreans more about film.

I thought of different films on the road to the mountains. One set at the end of the last world war. There were lots of people walking across frozen rice fields. Their clothes were drab. The looked like refugees.

You can understand why North Koreans don't want photographs. I saw bullock carts, a woman washing a pair of trousers in a hole in the ice of a frozen stream, people taking off their shoes and socks to cross a river. We passed a school. The glass in the windows was such poor quality that it looked as if it had been made from sheets of sugar.

North Korea must be the only country in world where a grammatical mistake could get you sent to jail

But what beautiful countryside. There are said to be 10,000 peaks in the Kumgang mountains. We walked for miles along river valleys, past icy waterfalls, and weird and strange rock formations like those in the film Picnic at Hanging Rock.

I remembered a science-fiction story I read at school, called, I think, Election Day. Rich tourists pay to travel back in time for dinosaur safaris. One man steps off the path, and accidentally treads on a butterfly. That causes a series of changes that cascade down the centuries. When he returns to the present, things have changed for the worse. A dictator has won the election.

'Spies'

I wanted to ask our North Korean guides - who seemed more spies than helpers - if they'd read it. Even that could have been risky. On an earlier trip a South Korean woman was jailed for a few days after she talked about North Korean defectors living in the South.

There are said to be 10,000 peaks in the Kumjang mountains

Even simple misunderstandings can be dangerous. When talking about Kim Jong-il you have to use the most honorific forms of Korean - or face punishment. It must be the only country in world where a grammatical mistake could get you sent to jail.

And the North Koreans seemed to be looking for offence. A soldier was found with a ChocoPie - a type of South Korean chocolate covered marshmallow biscuit. He said a tourist had thrown it from a bus.

The entire convoy of buses was detained at the tourist complex while guards questioned passengers. No-one owned up. We waited and waited and waited. Eventually one of the South Korean guides paid a fine in dollars and after an hour of waiting we headed back to the ship.

Pinprick in the border

Hyundai seems to be motivated by patriotism, not short-term profits. It's losing millions on the tours at the moment.

One Hyundai manager told me that all North Korea had supplied when building the tourist complex was sand, water and air. Even the sand wasn't very good quality.

The Korean staff in the tourist complex were from China. Even the "North Korean" food was made from ingredients shipped in from the South. Optimists talked of blowing a hole in the border when Hyundai started the tours to the North. Instead, he said, they'd just put a pinprick in it.

He said attitudes in North Korea meant that unification couldn't be achieved in a few years, as he first thought, but would take decades.

But if the company realises its plans to build ski resorts and car factories in North Korea there's bound to be more contact, which might finally lure the country out of its isolation and suspicion.

It might already be working a little. The film might yet have a happy ending. On the coach, we passed some children playing on a frozen pond. They'd made skates out of sticks and bits of wood, they were having a fantastic time.

They were the first North Koreans I'd seen smiling. I waved at them. They waved back.