Harrelson revealed slices of life in Supermax in conversations and in a series of letters to attorney Robert Tiernan.
"We struck up a friendship," Tiernan told ABC News. Eventually Harrelson came to describe his life inside.
"I promised to describe my cage and daily routine for you Bob. The cell is some 10' wide and 15' deep, 10' by 12' is the usable space. And then the bed, shower and commode/sink take up most of that," Harrelson wrote, noting that the one bit of the outside he saw was a slice of the sky.
"Part of the plan here is sensory deprivation," Harrelson wrote, his penmanship consistent and precise, Tiernan said.
Tiernan, who fondly recalls Harrelson as a "fascinating person, not very educated but very very smart, a real gentleman," noted that Harrelson was once deemed "a huge escape risk."
Not at supermax though, where Harrelson was something of an ideal inmate, gaining privileges such as a TV and radio over time. As a "tenant of this hospice," as Harrelson put it, he seemed resigned to the fact that there was no way out.
"I'm unable to exercise any control over anything outside this cage," Harrelson wrote. "I simply do my best with what I have."
Harrelson wrote that he generally ignored his opportunity to go outside for an hour and enjoyed the simple pleasures of a shower and reading "until the wee hours."
"The station that airs NPR in Colorado Springs switches over to the BBC radio broadcast each morning," he wrote. "It's my window on the world. I love it."
Tiernan, who visited Harrelson on a few occasions, noted a strange feeling in the contrast between Florence and the world his inmate friend called home.
As a visitor, Tiernan was led two stories down to a windowless room where he would wait, once for several hours, to see Harrelson. Tiernan characterized the experience as like being in a backward "Bizarro" world.
"The doors on the bathrooms lock on the outside instead of in. There is just no way out," Harrelson said. "And they go inside a pit, like an empty swimming pool, to exercise, so that you don't know where you are."
Harrelson, as a "cooperative" inmate, enjoyed his earned privileges inside, such as the ability to watch some television alone in his cell.
"I watch David Letterman's monologue. My other TV watching is nearly all CNN and/or PBS." He wrote that he liked "Nova," "Frontline" and "Nature," explaining to his pen pal and friend that life was bearable.
Tiernan noted that Harrelson managed to cope in Florence by taking pleasures as they came. "He enjoyed people coming to visit," Tiernan said.
"It could be infinitely worse," Harrelson told Tiernan."I could have been raised in one of those religious families. I could have been born in Darfur or Baghdad or Jerusalem or somewhere in another of those Third World countries where every bite of beans is a struggle," Harrelson wrote. "Hell, I could have been a Republican (shudder)! Those are only a few of the fates for worse than this one."
Harrelson died March 15, 2007, of heart failure. He was inside his cell at the time, of course.