The Burning Room, also referred to as the Bubble Room or the Basement, is a room inside the Crystal Temple that is first seen in the episode "Together Breakfast". It is used to destroy cursed objects in the central burner and houses bubbled gems.
The Burning Room appears to be located deep in the Temple's basement due to its direct connection with the Crystal Heart via a large crystal vein which runs down to it through Rose's room. There is a lava pit in the center which is used to destroy evil relics and other items. The room has gemstones floating in bubbles around the ceiling, which are the gemstones of Corrupted Gems and Cluster Gems. The Burning Room is opened by Garnet's gemstones, although it is not necessarily Garnet's actual room within the Temple.
Garnet tries to burn the Evil Spirit Scroll in the lava pit, but the monster escapes, absorbing the Together Breakfast and gaining "all the power of a breakfast". It then starts fighting the Crystal Gems before Steven defeats it by pushing it into the lava pool.
Steven is bubbled by Garnet and warped back to the Burning Room to protect him from a cave-in in the Ice Cavern. He quickly pops out of his bubble, then accidentally pops the Centipeetle Mother's bubble, releasing her and allowing her to regenerate. After she is "poofed" by a falling stalactite, Steven promises to find a way to heal her some day, bubbling her gem and a bag of "Chaaaaps" and warping them back to the temple.
Garnet can be heard opening the room in the background when Pearl and Garnet walk away from Steven and Amethyst.
After poofing Peridot and bubbling her gem, Garnet warps her back to the temple. Steven later uses the Crystal Heart's vein in Rose's Room to get into the Burning Room and pop Peridot's bubble so that he can ask her about the fear she showed at the Galaxy Warp. After being freed, Peridot panics at the sight of the bubbled gems, asking if the Crystal Gems are planning to "harvest" her before running away from Steven and escaping into the Beach House.
Steven releases Centipeetle Mother, along with the bubbled Bag of Chaaaaps.
At the end of the episode, Garnet and Pearl hold Bismuth's bubble before leaving it in the room.
Steven releases Bismuth from her bubble, who then reforms. Not knowing about corruption and believing the other bubbles contained all the Gems who disagreed with Rose, she releases Biggs Jasper before realizing she's not the same as Bismuth knew. Bismuth poofs Biggs with Steven's help, and Steven proceeds to tell her the truth about the Gem War.