Kindergarten

"Kindergartens" are facilities that serve to create Gems by using machines called Injectors. The "Prime Kindergarten" first appeared in the episode "On the Run". Underneath the Prime Kindergarten is the Prime Kindergarten Control Room.

Appearance
The "Prime Kindergarten" is a vast, foggy canyon with numerous holes carved out of the rock faces; which are the "birthplaces" of many Gems. Injectors dot the landscape, some of which have fallen to the ground and destroyed. The site has a single Warp Pad, which is decoratively surrounded by gems similar to those on the Injectors. It's also very scary, according to Garnet.

Background
The Kindergarten appears to be the reason why Gems invaded the Earth; to exploit its resources and produce more warriors via the Kindergarten for unknown reasons. It was once a flourishing center where Gems were grown and manufactured. If allowed to continue, it would destroy all life on Earth, as the developing gemstone would incubate in the planet Earth's crust and sap the life force from its surroundings to form itself. Rose Quartz saw the error in this, founding a faction of rebel Gems and leading an uprising that caused the Homeworld to cease the production in the Kindergarten, driving them off the planet at the cost of being forever stranded on Earth.

It is currently unknown what happened to the Gems produced there, but is possible that they were either destroyed, shattered, joined or absconded to Homeworld, or became corrupted Gem Monsters. Some Earth Gems, like Amethyst, appeared to have joined the Crystal Gems. Amethyst describes the reason for her joining the Crystal Gems as a desire to protect her birthplace.

Currently, the Kindergarten exists as a ruined canyon. There is a single Warp Pad, which can lead to any Warp Pad on Earth. The Injectors are out of use, although it should be noted that if the Kindergarten were reactivated, then these could be turned on for continuation of their previous project. However, Homeworld has different plans for the Kindergarten ever since their previous project was scrapped due to the war with the Crystal Gems. Their uses for the Kindergarten mainly involve their experiments for a Gem geoweapon as they use the location as incubation site for "The Cluster" and all its prototypes.

"Warp Tour"
Peridot briefly mentioned manually re-activating the Kindergarten, but was interrupted by a Flask Robonoid. After finding Steven's Crying Breakfast Friends sticker, she returned to Homeworld.

"On the Run"
Amethyst introduces Steven to this location. She reveals that she was made there, and that Gems used this place to create other "bad" Gems, or "parasites".

"Marble Madness"
The Crystal Gems follow one of Peridot's Plug Robonoids here. They later sever Peridot's connection to the control room, at the cost of her discovering their existence of on Earth. Pearl mentions Kindergarten has been inactive for 6,000 years and would destroy all life on Earth if reactivated.

"Keeping it Together"
The Crystal Gems go to the Kindergarten to search for Peridot. They find her, but she quickly escapes. Upon further investigation, Garnet discovers that Peridot wasn't trying to reactivate it, but instead she was checking on Cluster Gems, former Crystal Gems that Gem Homeworld shattered and forced to fuse, possibly as punishment for the rebellion.

"When it Rains"
Peridot shows Steven to the Kindergarten to give him more information about the Cluster, as well as referring to it as the "Prime" Kindergarten.

"Too Far"
Peridot, Amethyst, and Steven retrieve a drill head from one of the Injectors to use on their drill to the Cluster.

Trivia

 * "Kindergarten" means "children's garden" in German and usually refers to a place of preschool education. In this case, it literally means a garden where children are grown.
 * The area was destroyed by the incubated Gems around 6,000 years ago, as stated by Pearl in "Marble Madness".
 * In "How Are Gems Made?", it is seen that Gems suck the life out of their surroundings, and so mass-production of Gems in the Kindergarten left the location in a lifeless state.
 * It is unknown how many Gems were grown in the Kindergarten, and where most of them currently are.
 * Amethyst was grown at the Kindergarten, but joined the Crystal Gems sometime after the Rebellion.
 * Peridot has implied that the shards of Gems grown at the Kindergarten were used in the making of the Cluster.
 * The person-shaped holes on the sides of the Kindergarten, as well as the manner in which Amethyst slid into hers appear to be inspired by the Junji Ito horror manga, The Enigma of Amigara Fault.
 * Amethyst's hole is one of the few holes at ground level.
 * This is because she emerged 500 years later than all the other Gems grown there.
 * The Injectors resemble bacteriophages.
 * The body of the rig encases a structure that resembles an organic heart, which is attached to the head and feet via red and blue tubes resembling arteries and veins respectively.
 * The Prime Kindergarten created Gems of the Quartz variety, as revealed in Guide to the Crystal Gems.
 * Amethyst is a type of Quartz, and she was intended to be a (much larger) Gem warrior.
 * Peridot assumed that Steven was created in the Kindergarten because his gem is a type of quartz.
 * It was revealed by Peridot in "When it Rains" the Kindergarten looked much nicer in its prime.
 * As revealed by Peridot in "Too Far", Gems that stay in the ground for too long have stunted height when fully grown. An example of this would be Amethyst.