We know that the worlds each have a Heart and the Heartless were attempting to access said Hearts through the Keyholes but why do the the Keyholes exist at all? Why would the core of a world even have an access point that can be exploited? Are they ancient and forgotten maintenance hatches and the Hearts of worlds are just electrical grids? The fact that they can be locked and presumably unlocked means that at least someone is supposed to go in there for whatever reason. And why were they all left unlocked in the first place? You would think leaving the door to the very heart of existence unlocked would be a very bad idea.

That's actually a very good question, human! Perhaps that's one of those mysteries that Mr. Nomura will explain come Kingdom Hearts III? Or will we be left hanging when it comes to that, and the mystery of the Keyholes be forever left a mystery?

 

Or maybe these Keyholes date back from the Age Of Fairy Tales, and maybe the Keyblade Wielders of the Unions were supposed to keep the Keyholes in check and ensure they wouldn't be opened! I know it's a cheap explanation, but I can't think of any other reason! 

I think the Keyholes are just there as a part of the world...no particular reason. Just convenience. I mean, it's a part of the world in the same way oxygen is a part of ours...It's just there. 

Weirdomura will have to explain how those keyholes were created .

I don't think it's a deliberate design choice. If you think of Kingdom Hearts as the origin of all worlds and the blue print on which everything is based on, and it happened to have access to it in the form of a door opened by a key (accepting that the concept of doors and keys are not necessarily of man made origin in this universe so much as they are a natural formation), then it makes sense that all worlds, if an extension of Kingdom Hearts, would have the same default build within them.

You might be on to something with the whole "maintainance hatch" idea. Perhaps the Keyholes where deliberately created by the Dandelions who rebuilt the World after the Keyblade War as a fail-safe against Darkness. We know that Keyblade Masters have always been charged with protecting the balance of Light and Darkness in the World. Perhaps part of that was maintaining the hearts of the worlds via the Keyholes. Maybe they're supposed restore the balance of a world's heart if it's out of wack. In fact, that's pretty much what Data-Sora did in the Datascape. But maybe "Ansem", having once been a Keyblade Master himself, knew of this and used the Heartless' innate hunger for hearts to use the Keyholes to his advantage and do the opposite. We know that when the Heartless enter a Keyhole they do something to the world's heart, maybe that "something" is throw off the balance of the world's heart, allowing the darkness to consume the world. As for them being left unlocked, perhaps they are locked initially but are forced open when the wall surrounding a world is broken. There's definitely a link between the Walls of Light and the Keyholes because it was stated in the Ansem Report that when the Heartless "Ansem" was studying found Radiant Garden's heart, a meteor shower occurred the very same night and meteor showers like that one are caused when the wall is broken. So maybe if Keyhole is improperly unlocked the wall is broken and vice-versa. However, much of this is just conjecture based on the very limited information presented to us within the games, as we have no concrete answers from Nomura or Yasue.

Edited November 25, 20168 yr by Isamu Kuno

Well, a keyhole is like the heart of the world, and when it loses its heart, "they lose their minds and their feelings.  They're consumed by the darkness."  the purpose of the keyhole is kinda like the same as an individual and works pretty much the same except for 1 part, the ability to seal it and to allow inhabitants.  When Sora seals a world, the heartless cannot attack the world's core, so the world cannot fall into darkness.