The prison where the Guardians of the Galaxy are held is the Kyln. Nova Corps officers bring Peter Quill, Gamora, Rocket, and Groot there after their fight over the Orb on Xandar.
The Kyln is a high-security prison operated by the Nova Corps, the peacekeeping and military organization of the Nova Empire. Its inmates include Drax the Destroyer, who initially attacks Gamora because of her connection to Ronan the Accuser. Quill soon persuades Drax that Gamora can help him reach Ronan.
The prison is important because it is where the future Guardians first become a functioning group. Quill, Gamora, Rocket, Groot, and Drax cooperate on an escape after learning that Gamora has betrayed Ronan and plans to sell the Orb to the Collector. Their escape aboard the Milano begins their alliance.
The Kyln is sometimes confused with other Marvel prisons. The Raft is a high-security facility associated with Earth’s super-powered criminals, while the Vault is a separate Marvel Comics location. The Cube is not the prison used in this film.