Azkaban

Azkaban is the horrible wizard's prison where witches and wizards are incarcerated for their crimes. Located on a tiny island in the freezing waters of the North Sea, Azkaban is not like Muggle prisons that rely on iron bars and heavy security to keep their prisoners in line. Instead, until 1996 at least, Azkaban depended upon some of the most fearsome creatures on earth to guard its prisoners: Dementors.

Dementors are sightless, soul-sucking beings that feed on happy emotions and positive energy. Proximity to them causes people to relive their most painful memories. They take away every positive, happy feeling until a person is left wallowing in his or her own misery, unable to see any way out of the pain he or she is feeling. In essence, Dementors take away hope, and in the absence of hope most prisoners either give up the will to live or go mad. Trapped inside their own pain and incapable of even a single cheerful thought, the majority of Azkaban's prisoners went insane within a few weeks and eventually died.