The Eastern State Penitentiary in downtown Philadelphia looms prominently on the tourist map for people coming to the 2016 Democratic National Convention, but its doors are wide open. The first penitentiary in the US was shut down in 1971 and reopened in 1994 as a museum.

Aside from displays describing its long history since 1829, there is an exhibit titled Prisons Today: Questions in the Age of Mass Incarceration.

Since the 1970s, the US prison population has jumped more than 600 percent to well over 2 million. In terms of percentage of the population, more Americans are locked up today than in any other nation on the planet.

The message the exhibit seems to convey is that the mass incarceration system is broken, and to the nation's woe.

The penitentiary was set up through the advocacy of US founding fathers like Benjamin Franklin and a group of reformers known as the Philadelphia Society for Alleviating the Miseries of Public Prisoners. Their approach was a departure from the previous policy in the US, moving from punishment to promoting penitence.

But that approach diminished by the early 1900s as the system had to house more and more prisoners, including the notorious Al Capone.

On Tuesday noon, elementary school students were on a guided tour of the prison, listening to a guide talk about everything from Al Capone's cell to a synagogue and the exercise yard.

America's high incarceration rate and reforming the criminal justice system have been hot issues on the 2016 presidential campaign trail.

Vermont Senator Bernie Sanders has been decrying the criminal justice system for the past year. Speaking on Monday night at the Democratic National Convention, he said the election was about the leadership to repair a broken criminal justice system.

"It's about making sure that young people in this country are in good schools and at good jobs, not in jail cells," he told an audience that included many of his supporters.

The 2016 Democratic Party Platform, heavily influenced by Sanders, also calls for reform of the criminal justice system and an end to mass incarceration.

"Something is profoundly wrong when almost a quarter of the world's prison population is in the United States, even though our country has less than 5 percent of the world's population. We will reform mandatory minimum sentences and close private prisons and detention centers," the platform says.

"Whenever possible, Democrats will prioritize prevention and treatment over incarceration when tackling addiction and substance use disorder," it goes on.

Democratic presidential nominee Hillary Clinton and her husband Bill have taken a lot of heat for their records on mass incarceration.

The 1994 crime bill signed by then President Bill Clinton and pushed also by then first lady Hillary Clinton is widely regarded to have worsened the mass incarceration dilemma in the US with its harsh sentencing guidelines.