I *reeely* want to create the links between all the secret planes and the mortal realm. 

I had this cool idea that the only way for someone to get into X's plane is to wander around in a desert for 40 days and nights, and when the sun rises on the next day, you'll be in the realm of X. 
That way there's still the possibility that someone can find their way in by accident, but they're much more likely to die first. And then if they make it over, but die while walking through X's desert to the library, the bones can just pile up there. [i]which is eeextra spoooky![/i]

And the link to the realm of the dead would be through the reverse waterfall. Once you reach the summit by rowing a boat up it, your perspective flips, you're at the bottom of the waterfall, and all you see are dead people.