Oculus

The Oculus was built by the Elves as an "eye to another world". It allowed the Elves to harvest the incredibly potent mana flow of The End and use it to further their growth while also satisfying Yggdrasyl.

The Oculus was destroyed during The Quibilia Uprising, incidentally creating an explosion so strong, it rippled the frabrics of space and time, forever linking The End with the world.