You can access it once for each crystal you have and once you do, you can stay there for a limited time. About 1 min, I think. If you stand still, the darkness will slowly dissipate but, of course, you will be losing precious time. To get out elsewhere, you must stand still on top of one of the various scribblings on the floor. That covers everything I know about navigating the Disorder. There are also some secrets to be found there...
There is a room somewhere in the main world with a map of the Disorder. Lots of important information on that spot!