Atreia is the "planet" in the Aion universe where the game is played. Unlike planets of our universe, Atreia resembles two hollow hemispheres (or rather, "hemi-shells") with a single axle tower, the Tower of Eternity, connecting the centers of the two halves. Life flourishes inside the shell-like bowels, while the "surface" of the world is barren.
However, due to a catalytic event during the Millennium War, the Tower of Eternity is now broken, and rifts in the fabric of space known collectively as the Abyss now occupy much of the center of Atreia.The light from a nearby star reaches downward inside Atreia, illuminating the lower hemishell, where the kingdom of Elysea is located. However, little light reaches the harsh wilderness of Asmodae.