There's not too much information on C's World (World of C) or the imagery used in connection to it. It hasn't been officially explained so until a new canon Code Geass series is released (R3, a canon prequel like Jet Black Renya) the only information we have will come from the series and interpretations on what isn't fully explained.
What information there is all seems to point to how C's world is the "collective human unconsciousness" which is the source of the individual identities for all humans. Charles plan was to kill this so that everyone became a single identity (thus removing one of the main reason wars start) by using the Sword of Akasha, a temple-like structure which Charles refereed to as a "weapon" which was built by someone else as Britannia (particular Charles) only found it.
C's world is connected to both the living and the dead as when C.C shoots Mao she says
I'll see you again in C's World
Now we know that C.C's wish
was to be free of her immortality to be allowed to die
So her line assumes that when her wish is granted she would see Mao.
There's a Theory that C's World may be one of Jupiter's Moons or Jupiter itself as when the characters are at the Sword of Akasha and in the visions Lelouch sees we keep seeing Jupiter. However we can only assume that this planet is Jupiter because it looks like it. It should be noted that the times we see C's world is when the Sword of Akasha comes into play.
C's World also seems to be deeply connected to Geass as entry to it could only be done by/with the help of someone with Geass (Contractee or Code Bearer) as Suzaku is only brought to the sword by Charles or C.C. When Lelouch receives his Contract for C.C we keep seeing the same imagery involving Jupiter, the Sword of Akasha, and the Geass People.
Also, what was the guarantee that it would succeed?
It's implied that the collective human unconsciousness wanted Charles to succeed because it would have ended war since not once did it try and stop Charles or V.V but Lelouch influenced this to continue the march of time indicating the world would be stagnate and trapped in the past.
My own theory is that the Code made Charles untouchable as to activate Ragnarok originally required 2 Codes. (However after Lelouch saves C.C before Ragnarok is activated Charles is still able to activate it). Whoever built the Sword first probably knew that what happened to Charles and Marianne would happen to them so made it that the Code was required as well. While Marianne could have been killed at any time doing so would have done little to stop it so as long as one collaborator had the Code the plan would in some way succeed. Of course this relies on the fact that Lelouch's second sigil is a result of him obtaining Charles Code and that the Code can't be destroyed (thus why the Code Bearer who C.C got her code from said she had tricked C.C and forced the Code onto her).
At the current time C's World and the imagery used in connection to it hasn't been officially explained so until a new canon Code Geass series is released (R3, a canon prequel like Jet Black Renya) we won't have too much information to go by.