North Korea has three forms of political imprisonment. The short term forced labor camps are for those who have committed misdemeanors. The long term labor camps are for those who have committed felonies. And the Kwalliso are political penal labor colonies.
There are about 150,000 to 200,000 political prisoners in North Korea today. Unlike in countries like the United States, these prisoners are sent to the camps without going through any judicial process. And as a form of collective punishment, three generations of the criminal's family are sent to these camps with them.
Duties at these camps include tree felling, mining, timber cutting and other agricultural activities. Their sentences vary but some prisoners are forced to stay at these prison camps for life. There are believed to be about 6 prison camps in North Korea, and they're usually located in valleys in the country's northern provinces.