The Arkham Asylum for the Criminally Insane, typically called Arkham Asylum or simply Arkham, is an ailing psychiatric hospital – prison located in the heart of Gotham City.
Most if not all of Batman's rogues gallery have been sent to Arkham at least once over the years.
Years before the events of the series, while Harvey Dent was still Gotham City's district attorney and before Commissioner Gordon hit rock-bottom, the Joker was spending time in Arkham for his various crimes. New psychologist Harleen Quinzel was brought in to be his shrink, and more pressingly, figure out where in Gotham he had hid a bomb, set to blow up that night. Despite, believing she had gotten him tell him the truth, he had duped them all and the bomb was actually inside Arkham's chef, Luigi, who blew up, creating a hole in the cafeteria wall for the Joker to escape through. He took Harleen hostage but was eventually recaptured after Poison Ivy, who herself had managed to escape, saved them from a bullet and later surrendered to the Arkham guards.
In present time, Harleen, now Harley Quinn the Joker's girlfriend and sidekick, was sent to Arkham after a heist at a yacht with the Joker, where he left her behind in order to escape himself. She spent a whole year in Arkham, believing the Joker would come to break her out although Ivy, who had now become her best friend, tried to convince her he never would. The Riddler then provided Ivy a seed which she used to escape, and while she offered to take Harley with her, Harley insisted on waiting for "Mistah J", so Ivy simply knocked her out and took her.
After the events of "Lovers' Quarrel", the Riddler and Doctor Psycho were taken to Arkham, as well as Two-Face who had been held at the GCPD since he was overthrown by Jim Gordon during "There's No Place to Go But Down". Additionally, Harley checked herself in after confessing her love to Poison Ivy only to be shot down and for Ivy to choose to go through with her wedding to Kite Man. Her crew came to break her out so she could attend the wedding but she wanted to stay and "silently brood". However, Two-Face told her something was going to ruin Ivy's wedding and he would only tell her more if she helped break him out, which she did.
- Queen of Fables (escaped before arrival)
- "Til Death Do Us Part" (interior and exterior)
- "Finding Mr. Right" (interior)
- "Being Harley Quinn" (interior; inside Harley's mind)
- "A Seat at the Table" (interior; flashback to "Til Death Do Us Part")
- "All the Best Inmates Have Daddy Issues (interior and exterior; flashback)
- "Something Borrowed, Something Green" (interior and exterior)