Prison rig

The Prison Rig or Mining Rig was an offshore rig where Earthbenders were imprisoned and were forced to work with coal. It was run by The Warden. Built by the Fire Nation, this giant, stationary shipyard sits in the middle of the ocean. An enormous wall bisects the structure. On one side is a shipyard where the Fire Nation repairs and refuels its ships. The other side is a prison for the captive Earthbenders. The prisoners cannot bend because the metal rig is surrounded by water, and they are miles away from land. But the Warden doesn't let the muscular Earthbenders go to waste. He forces them to work in the shipyard, building new ships for the Fire Navy.

History
When Haru, an earthbender, was imprisoned and taken to the prison rig, Katara decided to be imprisoned too for save him. In the prison, she tryed to encourage the earthbenders into fighting back and winning their freedom but they had lost hope and decided not to fight the gaurds. Team Avatar came to rescue Katara, but she refused to leave until the other prisoners left too. Katara and Sokka blocked up all the air vents while Aang went into the boiler room and pushed the coal up, releasing it to the air vent the earthbenders were at. Katara the urged them to fight. At first the Earthbenders declined again. But, then, Haru thrown some coal at the Warden, who tried to attacked Haru with fire, but it was blocked by Tyro and three other earthbenders. The rest of the prisoners soon attacked the guards, pushing them back. Finally, the earthbenders pushed the firebenders into the ocean. After the victory, the earthbenders used the stolen ships to return to land.