Azkaban is a grim, formidable fortress located on a remote island, perpetually shrouded in cold and misery. Sirius Black described the experience of being imprisoned there as soul-crushing, stating that the worst part was not the lack of hope, but the loss of self, where one's happy thoughts and memories are slowly drained away until only the worst experiences remain. The constant presence of the Dementors meant that most prisoners eventually stopped eating and wasted away in despair. The island was not always a prison. Originally, it was the home of a little-known and extremely powerful Dark wizard named Ekrizdis, who practiced the worst kinds of Dark Arts. He lured Muggle sailors to his island, where he tortured and murdered them. After his death, the concealment charms he had placed on the island faded, and the Ministry of Magic discovered it. Investigators found the fortress infested with Dementors, creatures spawned from the misery Ekrizdis had created (Pottermore). Fearing that destroying the fortress would cause the Dementors to seek a new feeding ground on the mainland, the Ministry of Magic left the island untouched for years. It was not until Damocles Rowle became Minister for Magic that a proposal was made to use the location as a prison. He argued that the Dementors would serve as perfect, cost-effective guards, saving the Ministry considerable trouble and expense. Despite opposition, this plan was eventually implemented, and Azkaban became the official high-security prison for the wizarding world in Britain (Pottermore).
Azkaban serves as a constant, looming symbol of fear, justice, and despair throughout the series.