The cluster of shirtless, tattooed inmates in the prison courtyard make no effort to hide the joint as a policeman wanders by. Instead, one turns up the volume on the salsa booming out of a portable stereo. Unconcerned by the clouds of cannabis smoke billowing from the group, the officer does not miss a beat as he carries on patrolling the grimy maze of corridors and patios that make up Lurigancho, Peru's largest jail.
Built for 2,500 inmates, Lurigancho's crumbling walls are currently home to some 7,000 prisoners. Of Peru's 66 desperately overcrowded jails, this human clearing house on the arid outskirts of Lima is the most overcrowded.
Conditions are appalling. According to Peru's official human rights watchdog, the Defensoría del Pueblo, there are only 63 doctors and one psychiatrist attending to the country's 49,000 prisoners. Rates of HIV and Aids are three times higher than outside, and TB is 20 times more common.
Other than for sexual offenders, there is no segregation of inmates at Lurigancho. Armed robbers, hitmen and drug kingpins mingle with adolescents sent down for stealing a pair of trainers. Most are Peruvians but there is also a smattering of foreigners, everything from Africans to Americans, mainly convicted of acting as cocaine couriers.
Yet prisoners here have far more personal freedom than in most jails in the UK. They wear their own clothes, are allowed up to two conjugal visits a week, and from 6am to 6pm are largely free to wander around Lurigancho's labyrinthine facilities. Although there are several internal police checks, the biggest obstacles are the security controls organised by the prisoners themselves at the entrance to each wing.
"We don't want people we don't know from other wings coming here and causing trouble," one inmate tells me. "The prison authorities don't care, so we have to do it ourselves. Everything good here has been done by the prisoners. The authorities have just left us here to rot."
Inside, in the dingy corridors, inmates play cards and cook lunch on small gas stoves. Cannabis smoke scents the air, while stereos and old television sets are set to deafening volumes. In a nearby courtyard lies the prison "market", where entrepreneurial convicts trade fresh fruit and vegetables, used clothes and pirate DVDs. One rents out cellphones – supposedly banned by the National Penitentiary Institute (INPE).
In another courtyard, the walls are covered in murals. There are homages to Alianza Lima and Universitario, Peru's two biggest football clubs, both of which attract tribal, often violent, followings. Yet there are also colourful – if shaky – representations of Spider-Man and Winnie the Pooh, one of various poignant efforts made by the convicts to welcome their children on visiting days.
Meanwhile, just inside the main gate, two prostitutes negotiate with a group of inmates. Today is supposed to be a visiting day for men only – yet no one thinks anything of it until I ask one inmate. "Nurses," he says with a wry smile. Another tells me that without female sex workers, the prison would erupt.
Dreadful acts of violence occur here and Lurigancho is sometimes described as one of Latin America's more ferocious jails. Recently, one Dutch inmate was found to have battered and strangled his Peruvian girlfriend to death and entombed her corpse in concrete beneath the floor of his cell.
But Lurigancho is far less dangerous than many other prisons in the region. It takes only 150 police officers to supervise the thousands of inmates, even as they mingle freely together – conditions that would be unthinkable in jails in Central America or Mexico, housing some of the world's most vicious gang members.
Last month, the world watched in shock as more than 300 prisoners died after an inferno swept through a jail in Honduras. The blaze in Comayagua, about 45 miles north of the Honduran capital Tegucigalpa, was the country's third major prison fire since 2003. In Mexico, fighting between two drug cartels in February was reported to have led to the killing of more than 40 inmates at a prison near the Monterrey prison.
At Lurigancho, the incident with the Dutch inmate once again shone a spotlight on the corruption that, according to the Defensoría del Pueblo, is "institutionalised" in Peru's jails. Unresolved questions include how the prisoner acquired the sacks of concrete mix, and how was he able to spend hours banging his way through the rock-hard floor without the police guards stopping him?
Inmates with money or power inhabit well-equipped private cells, which, it is said, start at £2,000. Those without the means to bribe prison guards, convicts say, end up sleeping in the corridors. "You are like an orphan," one says. "INPE just dumps you here. They don't even give you a cell or a mattress. It is down to you whether you make it or not."
INPE also largely fails to live up to its legal obligations to provide vocational training and help prisoners prepare for release. There are huge pottery and textile workshops at Lurigancho, even exporting products to Japan. Yet these were set up by a non-profit group founded by the Catholic Church.
According to the prisoners who work there – and who ply me with gifts of their ceramics – guards levy bribes for raw materials brought into the jail and finished products brought out. The corruption is so rampant it is impossible to avoid even during a brief visit. To enter Lurigancho, visitors pass a series of security checks, with the police officers shamelessly, casually, blatantly demanding bribes.
"It's for a soft drink," one policeman says, demanding one Sol, roughly 25p, to allow me through. I demur but he insists. "It's hot today," he says. "I'm thirsty." Afterwards, a prisoner asks in disgust: "Who sells their dignity for a Sol?"
Unusually, Lurigancho is run by Peru's notoriously corrupt police. Yet if anything, the jails run by INPE personnel may be even more corrupt. Part of the problem lies in the lack of training or professional career path for INPE workers, according to Leonardo Caparrós, a former acting head of INPE. Promotion is based on the whims of superiors and there is no attempt to objectively judge job performance.
Meanwhile, INPE's top salary, including for the director of Piedras Gordas, the country's highest security jail, is the equivalent of less than £400. The police colonel in charge of Lurigancho earns around three times that amount.
INPE denied requests for an interview with its current boss, José Luis Pérez Guadalupe, as he battled to contain multiple corruption scandals, including a mass escape from Challapalca, a high-security jail at 13,000ft near the Bolivian border, often used to house recalcitrant prisoners from the coast.
Yet few in Peru, a country where many still live in grinding poverty, are willing to argue for more resources for convicted criminals. Meanwhile, populist politicians and tabloid newspapers regularly demand stiffer sentences when most criminologists agree that what is really needed is for the police to simply enforce existing laws. "The political use of jail adversely affects the proper functioning of the prison system," José Ávila, head of the Defensoría del Pueblo's prison programme, says diplomatically.
As I queue up to leave Lurigancho, the man behind me helpfully explains that I need to pay yet another bribe to avoid waiting hours for the police officer to return my ID. Behind us, as dusk settles on Lurigancho, the prisoners take one last breath of fresh air before filing into the heaving wings for the night.
Curious case of the president's brother
While prisoners across the region languish in appalling conditions, one high-profile inmate in Peru appears to be doing just fine, allegedly conducting business from his prison cell. Antauro Humala, the brother of the Peruvian President Ollanta Humala and a former army major sentenced to 19 years for leading a military uprising, has been making headlines after being transferred from Piedras Gordas prison to a secure unit at a military base.
The official explanation is that Humala's safety was at risk after the arrest of the leader of the remnants of the Shining Path terrorists, known as Artemio, who was also sent to Piedras Gordas. The authorities have not explained why they cannot protect Humala at Peru's highest security prison.
Revelations about luxurious conditions enjoyed by Humala and the supposed influence he wields from behind bars have sparked criticism of the president.
Fernando Rospigliosi, a former interior minister, called on the president to "acknowledge his responsibility for Antauro's privileges and announce his transfer to a common prison".
Antauro Humala's use of a prohibited cellphone and photos of him slow-dancing with his girlfriend have caused particular outrage. He has also been receiving business propositions from as far away as the US and China.
The allegations are just the latest in a long series of scandals surrounding the conditions of some of Peru's highest-profile prisoners, most notably Alberto Fujimori, the former president now serving 25 years for embezzlement and ordering extrajudicial killings.
Most of the revelations about Antauro Humala come from the hacking of his email account by Peruvian journalists. One email includes a "business model" for lucrative land deals. Correspondents also request his support for relatives applying for public-sector jobs.