Atreia

From AionSource.com Wiki

Concept art of Atreia

Aion's universe exists beyond the normal rationales of science. In the beginning, Atreia was once a single world. Its inhabitants lived inside the planet, on the surface of a hollow in the shape of a torus, intersected vertically at its core by The Tower of Eternity. After a cataclysmic event that occurred in the game's pre-history, the top and bottom halves of the world were disconnected and the Tower of Eternity was reduced to a shattered ruin.

The world of Aion resembles a globe, divided horizontally into two halves. The upper half is the world of the Asmodians, the lower half is the world of the Elyos. So basically the world-map of Aion is not on a horizontal plane, like a traditional fantasy world; instead it's vertical. With this in mind, some parts of both worlds can only be accessed from the air - such as floating castles, and islands in the sky. Because of this, all of the player characters can gain wings.

The area lying in between the two halves of Atreia is referred to as the Abyss. The Elyos's half is named Elysea, with the capital city of Sanctum, while the Asmodians' half is named Asmodae, with the capital city of Pandaemonium.