Waterbender prison

Hama's Prison, located on a remote island in the Fire Nation, is a maximum-security facility that was constructed specifically for detaining Waterbenders. To ensure that none of the prisoners had access to water, the guards had them suspended in cages, and dry air was pumped into their cells.

History
The Fire Nation ran prisons which were presumably created specifically to hold captured Waterbenders. The prisons were of high security, and went to extreme measures to ensure the prisoners could not escape, such as pumping dry air into the prison, and restraining Waterbender's hands whilst they ate and drank water, so they could not Waterbend. Any resistance or attempted uprising during this stage was met with severe consequences.



Hama of the Southern Water Tribe was brought here upon her capture from her home, and was the last Waterbender to be taken away by the Fire Nation. After staying here for most of her life, she discovered that during the Full Moon, her Waterbending powers increased drastically, to the extent of being able to control the water in blood inside of bodies, thus inventing Bloodbending.

After practicing this new art on rats in her cage, she successfully used the technique on one of the guards. This manipulated him into unlocking her cage; Hama then walked out of the prison as a free woman for the first time in many years.

Trivia

 * It was here that Hama first discovered Bloodbending, developing and mastering the ability by practicing on Elephant Rats. She escaped many years later by Bloodbending a guard to unlock her cell.
 * From Hama's flashback, it is generally assumed that her fellow Waterbenders from the Southern Water Tribe were held here as well.
 * In the scene prior to her duel with Katara, Hama, in her anger, stated that only she made it out of the prison, and that all her fellow Waterbenders failed to do so, implying that they died. She continued to state that the Fire Nation civilians "deserve the same".