The former commander, Abd al-Hadi al-Iraqi, led the 360-degree virtual tour of the site, Quiet Room 4, during a sentencing hearing at Guantánamo Bay that began last week. He described being blindfolded, stripped, forcibly shaved and photographed naked on two occasions after his capture in 2006.

He never saw the sun, nor heard the voices of his guards, who were dressed entirely in black, including their masks.

Mr. Hadi, 63, was one of the last prisoners to be held in the overseas black site network where the George W. Bush administration held and interrogated about 100 terrorism suspects after the attacks of Sept. 11, 2001

Even now, years after the Obama administration shut the program down, its secrets remain. But the details are slowly emerging at the national security trials of former prisoners at Guantánamo Bay.

In court on Monday, spectators saw Quiet Room 4, a 6-foot-square empty chamber, which Mr. Hadi said resembled the place he was held for three months — minus a bloodstain that was on the wall of his cell then.

Mr. Hadi described his conditions as cruel but said his experience as a prisoner of the United States had been tempered by remorse and forgiveness.

In 2022, the prisoner had pleaded guilty to war crimes charges. In addressing the jury on Monday, he apologized for the unlawful behavior of Taliban and Qaeda forces under his command in wartime Afghanistan in 2003 and 2004. Some used civilian cover for attacks such as turning a taxi into a car bomb. Others became suicide bombers or shot at a medevac helicopter.

“As the commander I take responsibility for what my men did,” he said in a 90-minute presentation. “I want you to know I do not have any hate in my heart for anyone. I thought I was doing right. I wasn’t. I am sorry.”

When he spoke of his time in C.I.A. custody, Mr. Hadi was describing the months after his capture in Turkey in late 2006, when he disappeared into the last remnants of the black site program, in Afghanistan, until April 2007.

At first he was held in a windowless cell with a built-in, stainless steel shower and toilet, as shown in the visual presentation in court. He was moved after months of constant questioning about the location of Osama bin Laden, which he said Monday he did not know.

The next cell, shown in court, was empty, without a toilet or shower — just three shackle points on the walls. For the three months he was held there, Mr. Hadi said, it had a thin mat on the floor, a bucket for a toilet and a splash of bloodstain on one wall.

At one point, he said, his food ration contained pork, which is forbidden in Islam. He refused to eat and became so weak that he could not stand. His captors then brought him a nutritional substitute, Ensure. He saw no sunlight and did not have a clock to know when to pray, he said.

The existence of the forensic photography was first disclosed in 2016 in the Sept. 11 case. Prosecutors gave defense lawyers the material but did not disclose the location of the last known intact prison of the black site program. Monday’s testimony made clear it was in Afghanistan.

The jury will decide a 25- to 30-year sentence for Mr. Hadi. But the sentence could be shortened by U.S. officials.

After another former C.I.A. prisoner, Majid Khan, was allowed to describe his torture at his sentencing hearing in 2021, his jury returned a 26-year sentence. But the panel also recommended he get clemency because of his abuse in U.S. custody. Mr. Khan has since been resettled in Belize and reunited with his family.

Last week, victims of attacks by Mr. Hadi’s forces testified to their continuing grief from the emotional and physical damage they suffered in the early years of America’s longest war. Monday, Mr. Hadi spoke to them directly.

“I know what it is to watch another soldier die or get wounded,” he said. “I know this feeling and I am sorry. I know you suffered too much.”

He appeared to single out a Florida man, Bill Eggers, who spoke of losing his firstborn son, a commando, in a roadside bomb set by Mr. Hadi’s troops in 2004. “I know what it is to be a father of a son,” he said. “To lose your son — your sadness must be overwhelming. I am sorry.”

Mr. Hadi opened his talk to the jury by apologizing for sitting in the padded therapeutic chair, rather than stand and address them. “I have problems with my spine,” he said.

When Mr. Hadi was first arraigned in 2014, he strode into court with a military police by his side. He is now disabled by a degenerative disc disease that, after the six surgeries, some unsuccessful, has left him reliant on painkillers, a wheelchair and a four-wheeled walker to move around.

He described his 17 years incarcerated at Guantánamo as lonely at times, an isolating experience interspersed with individual acts of goodness. While recovering from his surgeries, he said, prison staff nurses “cared for me with gentle kindness.”

During a period when he was left paralyzed, he said, a U.S. military doctor helped get him accommodations in his prison cell and “would come to play checkers with me, stay with me during my recovery from surgery.”