Image copyright AP

Koreans could once be sure that their children would look after them in their old age, but no longer - many of those who worked hard to transform the country's economy find the next generation has other spending priorities. As a result, some elderly women are turning to prostitution.

Kim Eun-ja sits on the steps at Seoul's Jongno-3 subway station, scanning the scene in front of her. The 71-year-old's bright lipstick and shiny red coat stand out against her papery skin.

Beside her is a large bag, from which comes the clink of glass bottles as she shifts on the cold concrete.

Mrs Kim is one of South Korea's "Bacchus Ladies" - older women who make a living by selling tiny bottles of the popular Bacchus energy drink to male customers.

But often that's not all they're selling. At an age when Korean grandmothers are supposed to be venerated as matriarchs, some are selling sex.

I can't trust my children to help - they're in deep trouble because they have to start preparing for their old age Mr Kim

"You see those Bacchus Ladies standing over there?" she asks me. "Those ladies sell more than Bacchus. They sometimes go out with the grandpas and earn money from them. But I don't make a living like that.

"Men do proposition me when I'm standing in the alleyway," she adds. "But I always say, 'No.'"

Mrs Kim says she makes about 5,000 Won ($5, or £3) a day selling the drinks. "Drink up fast," she says. "The police are always watching me. They don't differentiate."

The centre of this underground sex trade is a nearby park in the heart of Seoul. Jongmyo Park is a place where elderly men come to while away their sunset years with a little chess and some local gossip.

Image copyright Corbis

It's built around a temple to Confucius, whose ideas on venerating elders have shaped Korean culture for centuries. But under the budding trees outside, the fumbling transactions of its elderly men and women tell the real story of Korean society in the 21st Century.

Women in their 50s, 60, even their 70s, stand around the edges of the park, offering drinks to the men. Buy one, and it's the first step in a lonely journey that ends in a cheap motel nearby.

The men in the park are more willing to talk to me than the women.

Find out more Image copyright Thinkstock Listen to Lucy Williamson's report for Assignment on the BBC World Service on Thursday - or catch up later on the BBC iPlayer

Standing around a game of Korean chess, a group of grandfathers watch the match intently. About half the men here use the Bacchus Ladies, they say.

"We're men, so we're curious about women," says 60-year-old Mr Kim.

"We have a drink, and slip a bit of money into their hands, and things happen!" he cackles. "Men like to have women around - whether they're old or not, sexually active or not. That's just male psychology."

Another man, 81 years old, excitedly showed me his spending money for the day. "It's for drinking with my friends," he said. "We can find girlfriends here, too - from those women standing over there. They'll ask us to play with them. They say, 'Oh, I don't have any money,' and then they glue on to us. Sex with them costs 20,000 to 30,000 Won (£11-17), but sometimes they'll give you a discount if they know you."

South Korea's grandparents are victims of their country's economic success.

As they worked to create Korea's economic miracle, they invested their savings in the next generation. In a Confucian society, successful children are the best form of pension.

But attitudes here have changed just as fast as living standards, and now many young people say they can't afford to support themselves and their parents in Korea's fast-paced, highly competitive society.

Image copyright AP

The government, caught out by this rapid change, is scrambling to provide a welfare system that works. In the meantime, the men and women in Jongmyo Park have no savings, no realistic pension, and no family to rely on. They've become invisible - foreigners in their own land.

One Bacchus woman said to me 'I'm hungry, I don't need respect, I don't need honour, I just want three meals a day' Dr Lee Ho-Sun

"Those who rely on their children are stupid," says Mr Kim. "Our generation was submissive to our parents. We respected them. The current generation is more educated and experienced, so they don't listen to us.

"I'm 60 years old and I don't have any money. I can't trust my children to help. They're in deep trouble because they have to start preparing for their old age. Almost all of the old folks here are in the same situation."

Most Bacchus women have only started selling sex later in life, as a result of this new kind of old-age poverty, according to Dr Lee Ho-Sun, who is perhaps the only researcher to have studied them in detail.

One woman she interviewed first turned to prostitution at the age of 68. About 400 women work in the park, she says, all of whom will have been taught as children that respect and honour were worth more than anything.

"One Bacchus woman said to me 'I'm hungry, I don't need respect, I don't need honour, I just want three meals a day," Lee says.

Police, who routinely patrol the area but are rarely able to make an arrest, privately say this problem will never be solved by crackdowns, that senior citizens need an outlet for stress and sexual desire, and that policy needs to change.

But law-enforcement isn't the only problem.

Image caption Graffiti on a street on Seoul

Inside those bags the Bacchus Ladies carry is the source of a hidden epidemic: a special injection supposed to help older men achieve erections - delivered directly into the vein. Dr Lee confirms that the needles aren't disposed of afterwards, but used again - 10 or 20 times.

The results, she says, can be seen in one local survey, which found that almost 40% of the men tested had a sexually transmitted disease¬ despite the fact that some of the most common diseases weren't included in the test. With most sex education classes aimed at teenagers, this has the makings of a real problem. Some local governments have now begun offering sex education clinics especially for seniors.

Hidden in a dingy warren of alleyways in central Seoul, is the place where these lonely journeys end - the narrow corridors of a "love motel" and one of the grey rooms which open off them.

Inside, a large bed takes up most of the space, its thin mattress and single pillow hardly inviting a long night's sleep. On the bed-head is a sticker: for room service press zero; for pornography press three; and if you want the electric blanket, you'll find the wire on the far side of the bed.

So here you have food, sex, and even a little warmth all at the touch of a button. If only it were that simple outside the motel room, in South Korea's rich, hi-tech society.

But for the grandparents who built its fearsome economy, food is expensive, sex is cheap, and human warmth rarely available at any price.

Listen to Lucy Williamson's report for Assignment on the BBC World Service on Thursday - or catch up later on the BBC iPlayer

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