Moon Base

The Moon Base is an abandoned era 1 Diamond base on the Moon, built for the use of the Great Diamond Authority and other elite-class Gems to plan the colonization of Earth.

Description
The Moon Base is an ancient tower which served as the headquarters for the Great Diamond Authority to plan the colonization of Earth. On the first floor, there are murals of Blue Diamond, Yellow Diamond, Pink Diamond and White Diamond. The second floor is empty apart from a warp-like stream containing a blue spherical object in the middle of the room. The top floor is covered by a geodesic dome that allows a scenic view of Earth. In the center of the room, there is a raised platform with a single chair and a dashboard. The chair has a diamond communicator embedded in its left arm while the right arm has some of the controls used to access the computer and adjust the position of the chair. The top floor has a similar appearance to Yellow Diamond's Control Room.

Sub-areas
These are the three known rooms inside the moon base.
 * 1) Entrance way: This room is at the lowest known level of the moon base. The four diamond symbol is depicted on the floor with each of the colors directed toward the mural of one of the four diamonds. The control surface of the staircase is located on a certain tile at the edge of the room and composed a distinct material compared to the surrounding stone floor. Upon activation, it reveals the staircase which leads to the upper levels. The room's only known door leads to the lunar surface with a staircase outside, and it must remain closed to prevent the base's atmosphere from escaping.
 * 2) The Mapped Room. This room has a pattern of circles on the walls. Besides the detail, the exact purpose of the room is unknown.
 * 3) The Control Room: This room contains the central computer which holds information relating to the Cluster, the locations of the Kindergartens, as well as Homeworld's plan for the colonization and terraformation of Earth. 14 structures were originally built on Earth, which equals to 5% of the Homeworld's original colonization plan. Information stored includes The Cluster and blueprints for several other Gem structures including the Lunar Sea Spire, Ancient Sky Arena, Sea Shrine, Sky Spire, Communication Hub, Galaxy Warp, and two other unidentified planned structures.

"It Could've Been Great"
The Crystal Gems and Peridot traveled to the Moon Base for information on the Cluster's location in Earth. Steven activated the computer on the top floor, allowing Peridot to find it. Before they were about to leave, Steven asked Peridot if the computer had any games. Peridot explained to him that the Diamond's computer is used to contemplate the colony and for other serious purposes. She showed the Crystal Gems the plans for Earth's colonization, which upset them. Garnet destroyed the dashboard, shutting down the computer. When they were leaving, Peridot took the Diamond Communicator with her.

"Back to the Moon"
The troop of Rubies assigned by Yellow Diamond go to the base with the goal of filing a report after Jasper, who is really Amethyst in disguise, reveals she's willing to stay on Earth to keep the Crystal Gems under supervision. Eyeball, who was present in the war and in a constant attempt to impress her idol Jasper, reveals to the newest Rubies, Navy and Leggy, the story of how Rose Quartz shattered Pink Diamond, which is news to Steven, who is in extreme shock and denial. However, he's interrupted when the Rubies find the control room's dashboard completely destroyed, decide to leave with the promise to report to Yellow Diamond personally. But before they go, Amethyst accidently lets her form restore, revealing the ruse, and the Rubies, upset, fuse all together to fight the Crystal Gems. However, they're pulled into free space when Steven opens up the airlock and Sardonyx pushes them out with her hammer. Unfortunately, Steven is pulled out with them.

Trivia

 * Despite the base being made by and for Gems, the base appears to have some supply of oxygen as Steven, who is half-human, can breathe for the entirety of their stay there.
 * The presence of an atmosphere on lunar base make sense from the technical point of view: the atmosphere prevents the vacuum welding of mechanical parts, protect wires from overheating by dissipating the heat. The oxygen as an oxidizing agent is not the best choice, but it is presented in large quantities on the Moon, and can be easily extracted from lunar soil.
 * It could also be because in an empty vacuum with no oxygen, there is no sound, which would make verbal communication between Gems impossible.
 * Currently, the base has no active warp pad linking the base and Earth so the only way to get to the station from Earth would be to use an alternate means of travel such as a portal created by Lion.
 * In "Back to the Moon", it is revealed that the Moon Base was Pink Diamond's.