Pictures emerging of a Syrian soccer stadium turned into a coliseum of death by Islamic State terrorists are revealing the extent of the shocking horrors that once took place inside, as civilians reportedly were beheaded, tied down with iron cables and tortured by exercise machines.

The stadium in Raqqa, the ISIS capital city freed by U.S.-backed Syrian forces last week, has been called “The Black Stadium” for its dark, imposing concrete construction. But how it was used as a torture facility for the militant group gives the name a different connotation, The Daily Beast reported.

“The stadium became known for beheading people,” Issa Xabur, a 42-year-old civilian who used to live in the city, told the website. “It was used as a prison. Eighty percent of the people that were imprisoned here were killed.”

Recent photos of the facility show rusted out, destroyed prison cells and torture chambers ISIS built in the stadium's underbelly.

“It didn’t matter what you did or did not do, the ISIS police had 'good reason' to bring you in,” reads some of the graffiti written by prisoners, some in Arabic, Russian or English, according to The Daily Beast.

A reporter from the website who visited the stadium found iron cables and plastic straps used to tie prisoners down, while other reporters spotted exercise machines converted to bloody instruments of torture and death.

Xabur said he spent five days in the stadium and that people were arrested and sent there when they were “accused of being unbelievers, or of dealing with the coalition or the regime."

“They were hitting people with tires, and hanging people from the roof. People from Tunisia were responsible for torturing,” he said.

A British man who traveled to Syria to fight ISIS alongside the Kurdistan People's Protection Units posted images of the stadium on his Instagram account in recent days before he was killed while clearing landmines in Raqqa, his mother told Sky News.

“All in one place there was 3 tunnels, a lot of jail cells, a shooting range and a gym,” read Jac Holmes’ post on Oct. 22.

He added: “We spent weeks seeing this place from hundreds of meters away, it was strange walking the streets and finally going inside."