Go to the end of the world, and start from the save point "Final Rest". Go back through the portal, and defeat the 3 Invisibles, and 2 Angel Stars. After that, jump up and go through the top portal (all you are doing is back tracking), run down the corridor, and jump up again though that portal. Look around in this area, and you will see an image of a Castle. It looks like the picture of the Castle that Sora recognizes in Deep Jungle.