Kingdom Hearts series
Chain of Memories
Castle Oblivion was found by Xemnas of Organization XIII at this point, who decided to convert it into a second headquarters for the Organization. Marluxia was entrusted with control over it, but was secretly plotting to overthrow the Organization leader. After defeating Ansem, Seeker of Darkness, and restoring the damaged worlds, Sora, Donald Duck, and Goofy follow a path that leads into Castle Oblivion, which then forces them to fight through the castle to regain their memories. However, Sora's memories were being manipulated by a girl named Namine so that Marluxia could use Sora as a puppet against Xemnas. Meanwhile, Riku awakens within the basements of Castle Oblivion, and faces Organization members Vexen, Lexaeus, and Zexion to counter Marluxia's use of Sora, but they are all eliminated by Riku. Ultimately, the plan to control Sora fails thanks to the meddling of Axel, who frees Naminé, and Marluxia and Larxene are destroyed at Sora's hand. Sora then uses one of Xemnas's pods so that Naminé can restore his memories, and is eventually moved to Twilight Town. Riku is able to make it to the castle's top and discovers his friend's state, where he decides to depart from the castle to help while Sora is sleeping.
Because the game takes place during Chain of Memories, Castle Oblivion is mentioned when Roxas learns from Demyx and Xigbar that the members assigned to Castle Oblivion were annihilated. Xion later goes to Castle Oblivion seeking answers about her existence.
Kingdom Hearts II
The Castle's inside was seen in the opening credits of Kingdom Hearts II, featuring Sora's battle with Marluxia, Riku's battle with Ansem, Naminé's placing Sora in the Memory Pod, as well as several other important events in Kingdom Hearts: Chain of Memories illustrated in full computer graphics. The outside of Castle Oblivion was briefly shown in Roxas's final dreams, as Sora's memories end as he opens the door.
Birth by Sleep
The castle's origin is revealed in this game; it was initially the Land of Departure, but after the demise of Master Eraqus, it was available for the darkness to take over. However, Aqua returns to the remains of the castle and recreates the world into Castle Oblivion to prevent darkness from taking over the world. The new castle and layout would also be designed to keep unwanted visitors from gaining full access to it. From there, Aqua places Ventus in the castle's Chamber of Waking and departs.
Incorporated Films and shorts: Alice in Wonderland | Aladdin/The Return of Jafar | Beauty and the Beast | Big Hero 6 | Cinderella | Fantasia | Hercules | The Hunchback of Notre Dame | Lilo & Stitch | The Lion King | The Little Mermaid | Mickey, Donald and Goofy: The Three Musketeers | Mulan | The Nightmare Before Christmas | Peter Pan | Pinocchio | Pirates of the Caribbean: The Curse of the Black Pearl | Sleeping Beauty | Steamboat Willie | Snow White and the Seven Dwarfs | Tangled | Tarzan | Tron/Tron: Legacy | The Many Adventures of Winnie the Pooh
Villains: Master Xehanort | Ansem | Xemnas | Maleficent/Dragon Maleficent | Pete | Organization XIII | Vanitas | Xigbar/Braig | Xaldin | Vexen | Lexaeus | Zexion | Saïx/Isa | Demyx | Luxord | Marluxia | Larxene | Terra-Xehanort | Young Xehanort | Xehanort's Guardian
Other Characters: Jiminy Cricket | Naminé | Ansem the Wise/DiZ | Yen Sid | Xion | Axel/Lea | Master Eraqus | Dilan | Even | Aeleus | Ienzo | Lingering Will | Data Sora | Data Riku | Data Naminé | Data Roxas | Hayner | Pence | Olette | Riku-Ansem | Kairi's Grandma | Riku Replica | Anti-Saïx | Anti-Sora | Anti-Riku | Sora-Heartless | Jiminy's Journal
Disney Characters and Villains: Queen Minnie | Daisy Duck | Pluto | Tarzan | Winnie the Pooh | Aladdin | Genie | Tron | Magic Brooms | Peter Pan | Quasimodo | Judge Claude Frollo | Merlin | Tigger | Eeyore | Rabbit | Ariel | Mulan | Mushu | Jack Sparrow | Chernabog | Simba | Timon | Pumbaa | Nala | King Triton | Jafar/Genie Jafar | Alice | Cheshire Cat | Jack Skellington | Esmeralda | Phoebus | Beagle Boys | Scrooge McDuck | Huey, Dewey and Louie | Master Control Program | Sark | CLU | Rinzler | Beast | Stitch | Hercules | Tick-Tock the Crocodile | Snow White | Wendy | Ace "Chicken Little" Cluck | Baymax | Hiro | Rapunzel (More coming soon)
Objects: Sea-salt ice cream | Wayfinder | Door to Darkness | Keyblade | X-blade | Mickey's Letters | Thalassa Shell | Kingdom Hearts Encoder | Keychain | Gummi Blocks | Bug Blox | Black coat| | Keyblade Armor
Locations: Land of Departure | Disney Castle | Disney Town | Timeless River | Datascape | Radiant Garden/Hollow Bastion | Keyblade Graveyard | Destiny Islands | Traverse Town | Dive to the Heart | End of the World | Realm of Darkness | Castle Oblivion | Twilight Town | The World That Never Was | Castle That Never Was | Halloween Town | Neverland | Wonderland | Rapunzel's Tower | San Frantokyo
Music: Dearly Beloved | Simple and Clean | Sanctuary | Mickey Mouse Club March | Swim This Way | Part of Your World | Under the Sea | Ursula's Revenge | A New Day is Dawning | Destati | Bibbidi-Bobbidi-Boo | He's a Pirate | Beauty and the Beast | This is Halloween | It's a Small World | Night on Bald Mountain | Winnie the Pooh | The Sorcerer's Apprentice | The Pastoral Symphony
Soundtracks: Kingdom Hearts Original Soundtrack | Kingdom Hearts Final Mix - Additional Tracks | Kingdom Hearts II Original Soundtrack | Kingdom Hearts Original Soundtrack Complete | Kingdom Hearts Birth by Sleep & 358/2 Days Original Soundtrack | Kingdom Hearts: Dream Drop Distance Original Soundtrack | Kingdom Hearts HD 1.5 ReMIX Original Soundtrack | Kingdom Hearts HD 2.5 ReMIX Original Soundtrack