Remember the beginning of Kingdom Hearts? Sora is in a limbo-like shadow area standing on cathedral-like objects made of stained glass that show a Disney Princess in a scene from a movie.
Usually, if you were to be defeated by the heartless, you would start over from the beginning of the fight. However, if you're defeated on top of the Snow White cathedral, exactly in the center of the apple she's holding, you won't start before the battle.
Instead, Sora respawns in a different cathedra.
The first thing one notices about the area is the music. Instead of being choir-like or happy, as the music in the game often is, the music is nothing but this odd static sound accompanied by a single broken violin attempting to play a scratchy version of Simple and Clean. The longer one stays in this area, the louder the 'music' gets and even if the television is muted or turned down, it won't shut up.
As for the floor, it's like the Snow White one. The color of the glass is harsher and the scene is somewhat more frightening than the original, however. Instead of Snow White eating an apple, she is dead at the bottom holding the apple, blood leaking from all of her facial orifaces as the even queen laughs in triumph while holding a bloody heart.
As you progress in this new place, the other cathedrals have similar scenes: Beauty watches in horror as her father is devoured by the beast, Sleeping Beauty lies completely still with her face a gaunt gray (hinting at death, I assume) while King Philip is burned to death by Dragon Maleficent, Cinderella is sold into slavery by her step-sisters...
The scenes show what dark ending could have been put into the stories. The details in the pictures (especially the gruesome segments) are far more advanced than one would expect from a game of this time.
The Heartless you face in this area are also different. Instead of being cute shadows, they are horrifying. They have red eyes with yellow irises and sharp claws at the ends of their hands. They're taller than Sora and much more slender. They move insanely fast and often dispatch all but the most experienced players. They are also difficult to see, as the blend in with the black background. Most people are only able to see their eyes.
The staff and shield don't work against these creatures, so only people with the sword are able to fight them.
Most peole who randomly stumble upon this often reset the game, thinking it's a glitch because they're unable to get farther than the first cathedral. However, there are some who have made it much further.
The music gets louder (as mentioned before) and a strange whispering can be heard beneath the noise and violin. Finally, the player makes it to the last cathedral in the area and fights the giant Sora-shadow Heartless. He is different than the one you usually fight. There is no heart-shaped hole in his chest and his eyes are red with yellow irises.
The fight is rather short, as well. The giant grabs Sora, who gets wrapped up by the darkness. It begins to enter his eyes, nose, ears, and mouth. Sora screams while the violin plays louder, combining with the whisperings and other screams until it becomes a mess of noise...then the darkness covers Sora completely.
Most of the noise (save for the whispering) abruptly stops and the words "Game Over" flash continually on the screen. It's different from the usual game over screen, as it doesn't show Sora floating below his heart, nor does it have any options to return to the game or title menu.
Players who try to reset the game and start over find that every time they try to play that copy, all the screen shows is the Game Over screen with the whispering in the background. The few players who made it that far reported to hear whispering when they are alone in rooms and have occasionally seen red eyes with yellow irises in dark and distant places.
The designers of the game deny ever making this section and say the creatures, area, story, and music don't appear in the code. They claim it is a fabrication by people with a sick sense of humor.
However, there was one designer - Akane Hoyotami - who was on the game only in the beginning stages (when the cathedral levels were being created) and left shortly after this section was finished. Because he left so early, his role in the game is uncredited. He made some calls to the Japanese police after that, claiming there were creatures following him with red eyes and yellow irises.
The police dismissed his reports as the ramblings of a lunatic and led him out of the police station. He was found dead the next morning, cut up by something sharp. The neighbor in the apartment next to him claimed they heard Akane screaming about eyes and whispering when they called the police.