Within the first forty years of operation of the Soviet Gulag system, at least 18 million people were imprisoned, and more than one and a half million died. At its peak, the Gulag is comprised of nearly 500 prison districts.
Located in the heart of London on the River Thames, the Tower of London's reputation for torture and beheadings fuels nightmares. Originally built as a fortress by William the Conqueror in 1078, it becomes a prison in 1101.