Holy Pillar

The Holy Pillar is a divine occurrence that emerges somewhere on Luxendarc's after all of the crystals have been awakened perfectly. In Crystal Orthodoxy, it is thought that praying to the Holy Pillar will purge the world from darkness. Later it is revealed that when the Holy Pillar emerges, it actually creates an opening to other parallel worlds.

D's Journal
Added after approaching the Holy Pillar in Chapter 4

It is said that when all four crystals have been awakened, a pillar of light will appear somewhere in this world. Known as the Holy Pillar, it radiates with the First Light, divine source of life and the origin of this world and the heavens above. Airy claims that if she brings her brooch within the Holy Pillar, its divine light will sweep away all darkness and banish the Great Chasm from this world.
 * Pillar of Light: