On January 11, 2002, the first detainees arrived at Guantanamo Bay.
These "unlawful enemy combatants" were hooded and clad in orange jumpsuits. Their hands and feet were shackled as they shuffled in the stifling Caribbean heat.
The men were the first suspects in America's "war on terror". Most had been snatched from Afghanistan following the US-led invasion then sent to the American naval outpost on the south-eastern tip of Cuba.
It was a way of keeping them out of US federal courts – and denying them due process.
In its 20-year existence, 780 men – all Muslim – have been confined to the base’s jail, which started as hastily assembled chain-link cages and evolved into a multi-million-dollar maximum security prison system.
Gitmo, as it is often called, has been home to some of the world’s most wanted including the “9/11 Five," who are accused of helping Al Qaeda hijackers carry out the September 11, 2001, terror attacks that killed about 3,000 people.
But most of the inmates were released without ever being charged with a crime, and many observers see the prison's very existence as a stain on America's human rights record and its democratic principles.
Mr Worthington wrote The Guantanamo Files, and co-directed the documentary film, Outside the Law: Stories from Guantanamo with Polly Nash.
“The Close Guantanamo campaign was set up in 2012, to mark the 10th anniversary of the opening of Guantanamo,” Mr Worthington said.
“It seemed, at that point, to be so profoundly shameful, that the prison was still open.”
A decade later, Mr Worthington is still campaigning for its closure, but has little optimism US President Joe Biden will shut it down.
Immediately after taking office in 2009, Mr Obama signed an executive order to close the facility, something that Republicans fought tooth and nail. When Donald Trump was elected, he signed an executive order to keep it open.
The issue has long rankled Democrats and Republicans who are deeply divided over the fate of the jail.
In August, 75 House Democrats signed a letter saying the prison was a “two-decade human rights embarrassment” to the US.
In December, the brigadier general tasked with building the original metal cages in January 2002 said: “Guantanamo's creation and the urgency to gain information had bad consequences.”
Michael Lehnert, who retired as a major general, constructed the original prison system known as Camp X-Ray in under 96 hours. The Marine spoke candidly to senators about his regrets.
“Speaking plainly, we are where we are today because of those misguided policy decisions to cast aside our values and the rule of law,” Mr Lehnert said.
“I'm not an attorney, but even I know that when you forgo generations of legal thought and precedent, bad things happen.”
Mr Lehnert remains outspoken in his desire to see Guantanamo closed.
"They gave me 96 hours to open it, let's give them 96 days to close it," he told The National from his home in Northern Michigan.
For the lawyers who have toiled away working with incarcerated clients, most not even charged with crimes, the 20th anniversary is an uncomfortable and unfortunate milestone.
The damage – both physical and emotional – inflicted on many of the detainees is hard to overstate, said Wells Dixon, senior staff lawyer at the Centre for Constitutional Rights. Mr Dixon has represented men jailed at the site.
He urged Americans to “consider the damage that Guantanamo has caused to the United States, both in terms of its national security and in terms of compromising our fundamental values".
Jay Connell, who represents Ammar Al Baluchi, one of the “9/11 Five” who has been in pretrial hearings for more than a decade, has watched as the prison and military justice complex morphed into a sprawling permanent fixture at the naval base.
“We used to have just one small office with four computers in it and now we have a large office with something like 18 computers and so the military commission's infrastructure has grown,” he told The National.
Mr Connell said he has seen few on-the-ground policy changes during the past three administrations.
“There's a policy inertia around Guantanamo, where people just do it this month the way they did it last month for the most part,” he said.
“That's continued for at least the last 120 months.”
To date, Mr Biden has released only one detainee, who had been granted release under Mr Obama but because of clerical issues remained in custody for nearly five more years.
Abdul Latif Nasser, who was never charged with a crime, was released to his home country, Morocco, in July.
Today, 39 detainees remain at Guantanamo, which costs an estimated $500 million a year to operate. That means each detainee costs American taxpayers an estimated $13m per year.
The prison has outlasted America’s longest conflict, the war in Afghanistan.
Although Mr Biden was able to end the war, effectively allowing the Taliban to storm back to power, he has not shown the same political appetite for Guantanamo Bay.
About a year ago, when asked if the prison would be closed by the time Mr Biden leaves office, White House press secretary Jen Psaki said: "That's certainly our goal and our intention".
But with Republican opposition certain and the Democratic congressional majority likely to end in November, Guantanamo Bay is may remain open for years to come.