Cloud 9 was a massive vessel of unusual design that contained a five-star restaurant, theater, casino, several bars, and numerous hotel rooms and luxury suites. Its most notable feature was a huge biodome which contained a pressurized natural habitat nearly a quarter-mile in diameter, which simulated an outdoor park. The dome was mounted to the starboard side of the ship's main hull by a "V" shaped pylon structure which supported a spoon-shaped bow that contained the hotel. Behind the hotel section was a separately attached crew module which also contained the ship's hangar bay, command bridge, engineering, and sub-light/FTL drive engines. Directly under the saucer dome were another set of drive engines.
Inside the dome, many varieties of trees and plants from the Twelve Colonies were grown on the grounds and were cared for by a dedicated gardening staff. The dome also contained an artificial lake used for swimming. At the center of the park was a large auditorium structure used for gatherings and festivals. This building was used by Laura Roslin as the meeting place for the new Quorum of Twelve after the Cylon attack on the Colonies. The dome used any natural sunlight that was available, in an attempt to replicate the atmospheric conditions of a planet's sky. However, Cloud 9 was still a spaceship, and didn't really live up to the quality of a real planet, as there were some flaws in the design—such as fake terrain used to disguise the machinery as well as the easily noticeable and massive support beams of the sky dome. Despite this, Cloud 9 was judged to be one of the nicer places to live in the colonial fleet.
The ship was primarily used as a hotel and resort which had hosted various diplomatic functions and been the site of a terrorist assassination plot against President Laura Roslin, most notably during an electoral meeting for the Quorum of Twelve council, in which the radical Tom Zarek attempted to manipulate the council into voting him into the position of Vice President.
The ship had an "open port" policy and did not keep track of those who came and went, which caused numerous security problems and allowed members of the terrorist group "Demand Peace" to use it as a base of operations. Even President Roslin herself fled to Cloud 9 during Commander Adama's military coup.
Cloud 9 was destroyed in the Season 2 finale episode "Lay Down Your Burdens, Part II", along with at least three other ships including a Colonial Movers freighter. A nuclear warhead, which was given to the Cylon agent Gina by then-Vice-President Gaius Baltar, was used to destroy the ship. The shock wave from the nuclear explosion left behind an identifiable signature that was discovered by a Cylon patrol one light-year away. One year after the destruction of the ship, the signature led a Cylon invasion force to New Caprica.