Azkaban is a prison where wizards who violate the laws of the British wizarding world are sent. Only one other such prison, Nurmengard, is mentioned in the books. According to "Half-Blood Prince", Azkaban is "in the middle of the North Sea". Sirius Black says that when he escaped from Azkaban while in his animagus form as a dog, he swam to Britain and then travelled northwards to get to Hogwarts. This implies that Azkaban is at a lower latitude than Hogwarts, which is in Scotland. Although Azkaban's appearance is not described in detail in the books, it is mentioned to have grounds outside the prison where prisoners who have died are buried. In the film adaptations it appears to be a tall triangular building, somewhat hollow in the middle.