How do you get to crystal fissure in kingdom hearts 2?

To get to the fissure, you need to be at a certain point in the game. If you think you are far enough read ahead.

If I am remembering it correctly: Go out the door where the save point is (the one inside the house) and there should be some stairs to the right outside the door. At the top of the stairs is a doorway/archway, just go down the hall and down some stairs and it should be an area to the left that you can go to. Follow that pathway which should be some kind of path and you should eventually reach the fissure where there's a chest with the torn page and a save point.