Puerto Princesa, Philippines - Edwin Ymsom has already spent five years in prison for robbery and has another 10 years to go.

Although he is incarcerated, he openly sells cookies and peanuts to children at a swimming pool. Nearby, a few hundred prisoners armed with sharp-edged sickles cut grass.

The Iwahig Prison and Penal Farm in the Philippines is one of the world's largest open-air jails. Instead of concrete walls, the prison is surrounded by a wire fence. A single guard at the entrance gate greets tourists and criminals' relatives without inspecting them.

The prison and its 3,186 convicts are just 14km away from Puerto Princesa, capital of Palawan province, a top tourist destination near stunning dive sites and a giant underground river system.

Surrounded by a thick coastal mangrove forest and a mountain range, the 26,000-hectare jail - which is more than twice the size of Paris - offers a unique approach to reforming criminals.

"I stabbed a man to death," recalled 36-year-old inmate Effren Espinosa Jr as he waved a machete. "Here conditions are better than in other prisons, and guards treat us with dignity," he said before resuming his clearing duties in the garden.

As many as 200 minimum-security inmates are responsible for farming and office-related work, as well as for supervising the tasks of the medium-security inmates. Nearly 1,000 of the latter, who wear blue T-shirts, take care of the rice paddies, coconut plantations, corn fields and vegetable plots scattered across the prison grounds.

Only three armed guards - found leaning back in the shade of a faded roof - supervise thieves, murderers and other felons as they hack away the weeds.

Although it would take just half an hour to run away with their long cleavers, the inmates instead stand quietly in front of guards for the prisoner count, which takes place three times a day.

Aside from the maximum-security inmates, who are kept isolated, all convicts learn a trade, including farming, fishing, forestry and carpentry.

These income-generating activities allow the authorities to partially recoup the money spent on the prisoners' upkeep.

"The idea of this prison is to rehabilitate criminals, so that the minimum-security inmates feel integrated within the community. Our main mission is no longer only punitive but information and restorative justice," Iwahig's Superintendent Antonio C Cruz told Al Jazeera.

Created in 1904 by the American colonial government that ruled the Philippines at the time, Iwahig's location kept the most dangerous Filipino criminals isolated.

When the Philippines won independence after World War II, those who had served out their term were given the option to own land for free, depending on their conduct. Security measures softened in the 1970s, allowing some convicts' families to move inside the penal farm.

Today, only 20 minimum-security inmates live with their families inside Iwahig.

Convicts belonging to this group earn up to 200 pesos ($4.30) monthly, whereas medium-security convicts only earn half as much. An advisory board periodically reviews each case to determine a prisoner's status.

A portion of their earnings must be kept in a trust account until inmates finish their terms so they have some savings after being released.

Not all prisoners here are happy at Iwahig.

Twenty-nine-year-old Jeffrey, who sells his paintings at the prison, considers his sentence to be disproportionate: He is serving 15 years for stealing a car.

"I don't like it in here. My family can't come and visit because this island is too far from Manila," said Jeffrey, who also complains about food shortages in the prison.

Similarly, Araceli Gaddi, 62, criticised the prison's new regulations. "Rules are getting tougher. My husband can't live outside any more."

She lives in the hut set up for prisoners' families, but her husband has to sleep in the barracks. Since Gaddi moved to the colony in 1993 as the wife of an inmate, both her and her husband Dick were allowed to live together in a hut, where they raised their three children and a grandson. But that is no longer an option.

Although penal farms see fewer escape attempts than other Philippine jails - only 20 have occurred at Iwahig in the past decade - a successful June 2014 jailbreak of seven prisoners led authorities to forbid convicts from sleeping outside the barracks.

Some inmates have alleged deficiencies in the prison's management.

A report from the Philippines' Ombudsman published in 2007 - the last year the report was published - noted "political patronage or bribery" in the colony, as well as a lack of transparency regarding the prisoners' income generated by the farm.

The report singled out "Balsahan", the natural swimming pool at Iwahig. Although tourists are charged an entrance fee, the report stated "there is no official receipt or any proof of payment issued to paying visitors … Therefore, there is great probability that corruption may occur".

But James Ali, the father of one of the children swimming in the pool, said concerns such as transparency are trumped by the benefits offered at this prison without walls.

"I don't think they're bad people," he said, pointing at one of the inmates. "Anyone is capable of doing what they did if forced by the circumstances. Everyone deserves a second chance".

Follow Angel L Martinez Cantera on Twitter: @AngelLMartnez