Asylums are hospitals specializing in the care of those suffering from mental disease and distress. In fictional worldbuilding they often serve the criminally insane, those with psychic powers, and tortured artists who have glimpsed terrible cosmic truths about our world. Asylums may also imprison entirely sane protagonists that are held at the mercy of an insane system. Asylums are generally located in rural or hard to reach locations. They contain cells, drug dispensaries, gardens, solitary confinement wards, mess halls, offices, nurse stations, and other areas. They are home to therapists, the criminally insane, mad doctors, regular doctors, patients, and hospital staff. They are often used as a haunted location.
Caution: Fictional asylums are depicted as very different places than their real world equivalents. Real world mental health is an important and nuanced topic. Take care of yourself and others.