By Daniel Schweimler
BBC News, Buenos Aires
La Plata is a lovely city. Its central plaza is dominated by a beautiful cathedral, its tree-lined streets are full of interesting shops and quality restaurants.
Some call La Plata the prostitution capital of Argentina
It is a thriving university city and the capital of Buenos Aires province - the largest and wealthiest in Argentina.
But there is also a sinister, sleazy underside to La Plata.
Some call it the prostitution capital of Argentina.
In and around the city there are hundreds of brothels, incongruous from the outside - in residential streets, at the bottom of dirt roads - often only recognisable by a straggly array of coloured light-bulbs or a barely visible name.
Susana Martinez is a former prostitute who now helps to run the Sandra Cabrera health centre in the city.
It is a health centre run by sex workers for sex workers.
It was set up two years ago, with the help of the local authorities, after prostitutes, rent-boys, transvestites and transsexuals complained they were suffering discrimination in the public hospitals.
Sandra Cabrera was a campaigning sex worker killed by the police in a still-unresolved case.
Sex workers' needs
"They would shout things like 'You deal with the whores,' or 'Look what's blown in with the rubbish,'" said Susana.
She added that sex workers also had different medical needs and worked different hours to other people. The public health system simply was not serving their needs.
A recent study in Argentina also found that one in three people did not know how Aids and the HIV virus were transmitted.
This in a well-informed public after more than 20 years of campaigns and advertising.
So former sex workers, like Susana, and those still working, like Mishel, work with the medical staff at their health centre to build trust with the patients and to educate as well as treat.
"We needed to educate and to make people aware of our specific problems but also to tell them not to discriminate because of the work we do," said Susana.
Susana Martinez does twice-weekly visits to brothels
"One day a colleague told me that our doctor, while doing the check-ups, tried to persuade the girls to leave prostitution and the streets.
"I was angry because we are free to choose. I've never told them to stop being doctors and change profession.
"So, as you can see, it was hard work to make everybody aware and respectful."
She added: "We also had to educate the nurses. They were terrible. They'd come from hospitals where it's common to shout and maltreat people."
Many of the prostitutes that come to work in La Plata are from Paraguay and Peru or the poor northern provinces of Argentina.
They are usually young, sometimes too young to have sex legally, and nearly always badly educated and frightened.
Twice a week, Susana does the rounds in a mini-bus, visiting the brothels and talking to the prostitutes. She distributes condoms and tries to find out how the young girls and boys are doing, how they are being treated.
They cannot go everywhere and some places are simply too dangerous for them to visit. Much of the sex industry in La Plata is operated either outside the law or on the very edges of the law.
The health workers asked me not to film or record, to keep my mouth shut and, if asked, say I was from the health ministry.
The first place we visited was down a dirt road, outside the city.
Its name was displayed in dull purple lights. Loud music blared from inside. There were pool tables, an empty stage and a silver disco globe.
The young owner behind the bar eyed us suspiciously. Susana, bubbly and friendly, greeted him and the two girls sitting silently on stools at the bar. One kept her face hidden, the other sipped her drink nervously. Both wore short skirts and high heels.
It was early and work had not yet begun. Two men playing pool made phone calls then walked to the far side of the almost empty room.
Susana plonked a bag of condoms on the bar and asked the owner to sign for them, which he did.
Susana asked if she could talk to one of the girls in private and after five minutes returned. The girl, from Paraguay, was pregnant.
Some are kidnapped and forced into the sex industry. Others are tricked with offers of jobs as domestic workers or waitresses only, on arrival in Argentina, to have their documents confiscated and their freedom curtailed.
With no money and no ID, there is nowhere to go. Families back in Paraguay or northern Argentina are poor and often working away from home themselves. And the local police are some of the main beneficiaries of the industry.
Susana knows where the underage girls and boys are working but, she said, while the authorities are so closely involved in the industry there is nothing they can do to change the situation.
Through their health centre they can at least provide education, protection and condoms - plenty of condoms. They distribute 20,000 a month, paid for by the local authorities.
After visiting the brothels, we toured the dark streets.
Firstly, the area where the female prostitutes work, then the male ones. The mini-bus pulls up and Susanna leans out of the window waving a plastic bag full of condoms.
"Protection, condoms!" she shouts. Many of the workers know Susana, recognise the van and come sauntering over with a kiss, a joke and a bit of gossip.
Others, new to the city, are more wary. Susana asks them how they are doing, if they need any help and tells them where the health centre is.
Then we move on to the area where the transvestites and transsexuals work, precarious on high heels, displaying buttocks and breasts, giggling and mocking one another.
"They're all Peruvians," said Susana.
Condoms are handed out to sex workers at brothels and on streets
According to Mishel, one of the reasons the industry has thrived in La Plata is that the authorities allow it, often encouraging it to do so.
He lives and works in a house in the centre of the city with 13 friends, both men and women, including a married couple. It is a co-operative. The rooms are clean, they advertise in local papers and can afford one another some kind of protection.
But the police insist that they too provide protection. Mishel pays the local force $400 a month. "Otherwise," he said. "They've said they can't protect us."
"From who?" I asked him.
"From third parties," he replied. "I don't like it but there's nothing else I can do if I want to continue working."
Mishel, like all the sex workers in La Plata, has a story to tell. He is from a small, conservative town in rural Buenos Aires province. His relationship with his mother deteriorated when she realised he was gay and, as a young boy, he left for Buenos Aires.
There his only option was to work the streets. But one day he was picked up by a person who he thought was a client.
He spent the next nine years as a sex slave, forced to sleep with whoever his owners told him to - often servicing guests at the city's five-star hotels.
"It was wealthy businessmen," he explained.
"Often foreigners and even diplomats. They knew I was underage. I got nothing. Maybe some perfume or a couple of pesos."
He finally escaped and went to live with his brother who was studying in La Plata.
After working for a while in a burger bar, he went back on the street. It was the only way he could earn enough to study and to pay for his brothers and sisters to study.
The Sandra Cabrera health centre has become a model. They receive visits from other parts of Argentina and from abroad. It can do nothing to tackle prostitution in La Plata.
Those, like Susana and Mishel, know the industry only too well, they know it is deeply ingrained in Argentine society and they are powerless to help.
But they do know what problems the city's sex workers face. And they do provide some protection, plenty of understanding, medical care and advice and some hope for people living on the margins of an often cruel and uncaring society.