Intensive Treatment Center

The Intensive Treatment Center was the initial building of Arkham Asylum. It housed Holding Cells, a Patient Pacification Chamber, and even a Decontamination Room.

Originally, the center was a factory before the asylum had been constructed. There had been many suicides reported there.

Arkham Asylum Incident
It was here that The Joker was being transferred back to his cell. As the Joker was being escorted by a doctor and a security guard through the Holding Cells, he broke free and killed both men. Batman, watching from a reception area, crashed through a window in pursuit. The Joker loosed all the Blackgate Prisoners in the Holding Cells to attack Batman. Joker then made his way through the Processing Corridor, and killed four security guards in the area.

Joker continued to the Decontamination Chamber while the remaining security personnel were preoccupied with trying to recapture Victor Zsasz, who had already murdered a guard in the Patient Pacification Chamber and was holding another, Mike, hostage. After Batman had arrived on Joker's trail and subdued Zsasz, the Arkham staff retook control of the Patient Pacification Chamber. Meanwhile, the Joker had filled the Decontamination Chamber with his toxic gas, which killed escaped convicts and security guards alike, and left only four survivors, who had managed to climb to safety. The Joker continued on to the Transfer Loop, killed more security staff, and vandalized everything with spray paint.

Joker then proceeded to the Secure Treatment Transfer with several of his men, who overwhelmed the guards. The Joker let loose a mutated Blackgate Prisoner on Batman, who died of natural causes after fighting the Dark Knight. The Joker escaped through Extreme Isolation, and the sole surviving security guard was not able to allow Batman through, due to the fact the Joker had rendered the computerized transport system to Extreme Isolation unusable. Around this time, corrupt security guard Frank Boles, kidnapped Commissioner Gordon and took him through the Transfer Loop and into Secure Transit with Harley Quinn. Another security guard, Henry Smith, attempted to follow them, and found that someone had jammed the elevator controls.

On the upper level, a team of Joker's Henchmen had seized control of the elevator area, which had been further disabled by Harley Quinn in an effort to slow Batman down. Armed convicts, meanwhile, had wrestled control of the Cell Block Transfer section from the guards. With the situation spinning out of control, William North and a security team were still guarding the Intensive Treatment Lobby, oblivious as to the impending situation. Boles betrayed them, and killed at least three guards. An army of Blackgate Prisoners finished off the rest of the guards while North fled to the Utility Corridor. Batman arrived on the scene, and, shortly after, re-secured the area and found Boles dead, betrayed himself by his employer, the Joker.

Later, as Poison Ivy's plants began to overrun the island, the Blackgate Prisoners returned and recaptured the Intensive Treatment Lobby. The Intensive Treatment Center by that point became heavily damaged by Ivy's mutated plants. Batman returned to the Cell Block Transfer section, where Scarecrow and an army of Blackgate Prisoners ambushed him. Batman followed Scarecrow back into Secure Transit and defeated the remaining henchmen. The Intensive Treatment Center was liberated by the GCPD as the police retook control of Arkham Island after the Joker's defeat.

Arkham Knight Incident
While the actual location was not shown, Batman had his final confrontation with the Joker inside a imaginary version of Intensive Treatment inside his head. This version only consisted of one walkway surrounded by several hanging cells and infinite emptiness. As Batman overcame his Joker Infection and got over the guilt of failing to save the Joker back in Arkham City, he locked the memory of Joker inside a cell, and gave it enough momentum to slide behind a set of giant doors, which locked Joker away from his memory, forever.

Trivia

 * This was the very first location seen in the Batman: Arkham series.