Omar al-Shogre spent three years in 10 Syrian government prisons, where he was tortured and starved - and yet he describes his imprisonment as "the most beautiful days of my life".

On June 11, 2015, Shogre saw light for the first time in nearly three years. He weighed only 35kg and had no hair left. When he said hello to people on a bus near Damascus, no one replied; they were too busy looking at the wretched figure in front of them.

A year later, in a checkered shirt and jeans, Shogre runs along the waterfront in Stockholm, stopping to buy a sticky Swedish bun. Behind him, families queue for the roller-coasters at the central Grona Lund theme park.

Shogre, 21, was among tens of thousands of people jailed in Syrian regime prisons. More than 17,000 people died in custody across Syria between March 2011 and December 2015, according to Amnesty International, while the United Nations has accused the government of President Bashar al-Assad of committing "the crimes against humanity of extermination, murder, rape … torture [and] imprisonment".

Shogre was arrested at 17 in Syria's coastal province of Tartous in November 2012, along with three of his cousins. Two of them would later die in prison. He says that he does not know why they were arrested that day; soldiers showed up at his aunt's home with no explanation, struck Shogre in the face until he was "pouring blood", and hauled the group off to jail.

Moved between 10 government detention centres, Shogre ended up in the notorious Sednaya prison, wedged into the craggy mountains 30km north of Damascus. He spent a year and nine months in Branch 215, a military intelligence detention centre in central Damascus known among some Syrians as the Branch of Death.

"We used to see when a prisoner was forced to have sex with another prisoner, or when a head of a cell was raping another prisoner," Shogre told Al Jazeera in a matter-of-fact tone. "Everybody used to be afraid of it. I always used to think about it, especially because I was very young. I thought that soon they would do it to me."

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For the first seven months, Shogre was kept in solitary confinement. Later, he watched as sick prisoners were picked off and locked in a room, visible to other prisoners. Those who fought to live were beaten until they would fight no more.

Torture and death became normal. "A lot of people were being raped and killed themselves as a result. It is horrible, but it became something normal," Shogre said. "The person who was being raped was only a body for us, just like all the people who were being killed and tortured."

Sednaya would be Shogre's final prison, and the worst. His "welcome party" on August 15, 2014, involved a beating with tank tracks. He grimaces as he remembers it: "There were 10 of us in a row and [an officer] started to hit us, one after the other. For 15 days, I could not open my eyes or get up."

A month later, Shogre was taken to court, where a five-second trial led to his conviction for "terrorism" offences - the charge used against scores of anti-government activists by the Syrian regime. Shogre, who had taken part in anti-government protests during the 2011 revolution, says that he was forced into a false confession of forging ID cards.

The food was always mixed with blood in Sednaya prison. At least the blood had some salt in it. Omar al-Shogre, former Syrian prisoner

When prison guards brought the day's food rations - a few eggs and some bread to share among several dozen prisoners - they came equipped with metal sticks to beat the prisoners. "The food was always mixed with blood in Sednaya prison. At least the blood had some salt in it," he added wryly.

Amnesty International, which has conducted extensive research on Syrian prisons, said that the experience Shogre described was typical. Many detainees were able to recall specific dates and vivid details of what they endured, said Nicolette Boehland, who has led the organisation's work on Sednaya.

"Many of them know it might be useful later - and memorising them is almost like their act of rebellion, or a way to retain dignity," Boehland explained.

Shogre's nights are still filled with memories of the horrors that he endured.

"When I sleep, I dream a lot of me being tortured. I see my cousins being killed. When I wake up after all these horrible dreams and find myself in my room and not in prison, I am so happy," he said.

But today, as he sits at the edge of the lake next to his new home in Sweden, he whistles loudly and smiles, watching a white bird fly low over the cobalt water.

"They were the most beautiful days of my life, prison," Shogre mused. "I became human. It was the best university. I entered prison as a child and I learned how to live."

Although he still despises the guards who tortured him, Shogre says that he also saw the best of humanity while in prison. Other prisoners helped to save him, giving him their food rations so that he could live, and paying guards not to kill him. Although practising Islam was banned in Sednaya, he silently memorised 18 chapters of the Quran during his time in confinement, taught in whispered exchanges with other prisoners.

Today in Sweden, "I see things here that people are afraid of, and they are very normal to me compared to what happened in prison ... [But] if I was always happy, then I would not know the meaning of happiness any more."

The path towards Shogre's eventual release from prison began in May 2013, when two of his brothers and his father were killed in a massacre. His mother and remaining siblings fled to Turkey, where they scraped together the $15,000 bribe needed for his release.

In June 2015, he was issued with a letter confirming that he would be released after serving a quarter of his three-year-and-four-month sentence of "temporary hard labour" for his "terrorist activities".

His time in pretrial detention was not counted against his sentence, the length of which he had not been informed; he was expecting to die in Sednaya.

Upon his release, Shogre was blindfolded, driven outside the prison perimeter, and made to crouch by the roadside before his jailers let him go.

Although his family was in Turkey, Shogre opted to restart his life in Sweden, where he would be able to access necessary treatment for the tuberculosis that he contracted in prison. In Stockholm, Shogre now has a warm home and compassionate friends, but he remains wary at the knowledge that the Syrian regime may try to take revenge for his public comments about the realities of Syria's prison system.

"I am always waiting for what is going to happen to me next," he said. "When I was in Branch 215, I was freer. But now I am not free, because I am just waiting and waiting and I do not know what will happen to my family next."

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The support networks available to Syrian former detainees are relatively limited, and some, including Shogre, choose not to access professional help.

Psychiatrist Jalal Nofal, who himself spent nearly nine years in Assad regime detention in the 1980s, says that the main issues among former Syrian prisoners are depression and anxiety.

"We encourage people not to see themselves as victims, but as survivors, and to look for their strengths," Nofal told Al Jazeera. "[Sometimes] they think, 'How am I free, laughing, eating well, when my comrades are still suffering?'"

For now, Shogre knows the difference between being alive and being human. He feels that he is both.

"I do not know how I am still alive," he said, walking along the lawn by his new Swedish home as the sun dipped lower in the sky. "It is impossible to believe. I think of that, sometimes, when I wake up in the morning."