Eastern State Penitentiary - once the world's largest and most expensive prison

When it opened in 1829, Eastern State Penitentiary was described as the largest and most expensive prison in the world and became the model for over 300 prisons worldwide. The facility pioneered the radial 'hub-and-spoke' design and the Pennsylvania system of separate confinement intended for prisoner reform. It later housed notorious inmates such as Al Capone before closing as a prison in 1971; it now operates as a historic site and museum. The penitentiary's architectural and penal innovations had international influence on prison construction.