Greenland's Nuuk maximum security prison houses extremely dangerous prisoners, many of whom grew up alongside the guards now watching over them.

Once again, Raphael Rowe volunteers to go behind bars, this time in the Philippines at Manila City Jail, one of the world's most overcrowded prisons.

At Brandvlei Correctional Centre in South Africa, nearly all the convicts belong to dangerous gangs known for lethal stabbings.