Behind Bars: The World's Toughest Prisons

Colony 100 in Kharkiv, Ukraine, is a prison for hardened criminals. Inmates are either repeat offenders or have committed crimes so heinous, they'll never leave their 100-square-foot cell again.

The Philippines' South Cotabato Provincial Jail houses over 2,000 inmates. President Duterte's war on drugs overwhelms the system, putting the guilty and innocent behind bars together.

Inmates at Carcel Distrital in Bogota, Colombia, fight many battles. A strict approach is necessary to keep prisoners in line, especially when nearly 1,000 of them aren't used to rules.

Armenia's Armavir Prison is controlled by a mysterious criminal brotherhood. However, the prison is the first attempt at limiting their influence by locking them in dedicated blocks.

La Mesa, a Mexican prison just over the US border, houses tough criminals that hardly get to leave their cells. The facility is ruled with an iron fist so its infamous history can never be repeated.