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The Dimensional Pillars are strange towers that can transport the user of the tower through time and space, with no ill effects to the space-time continuum as all encounters are written in the Legend Books. Every tower has a different location or time, with some transporting Ender several millennia into the future to another galaxy, and others just throwing the user across the planet.
Every tower has a different "Alter", meaning that whoever enters the tower takes on a form chosen by the tower. It's a strange process, and nigh impossible to explain without breaking the fourth, and possibly fifth, wall.