Athas

Athas was a desert planet located in a crystal sphere that was cut off from the rest of the Prime Material plane. Travel to and from the sphere was impossible by physical means and extremely difficult even by magic.

Geography
The crystal sphere that contained Athas was not connected to any of the usual spelljamming routes out of Realmspace, Krynnspace, or Greyspace. Its location in the phlogiston was not documented in any book or chart. Some speculated that the crystal sphere was simply too distant from known space, so much so that traveling there would take several lifetimes.

The world's inaccessibility was the result of a property of its crystal sphere that rendered it impenetrable to spelljammers and almost completely cut off from other planes. The border of the Ethereal plane within the sphere was replaced by an environment known as "the Gray", which caused anyone in it to become lost and slowly weaken. It was extremely difficult to overcome by planar travel even by powerful spells such as teleport without error and plane shift, which had a risk of sending the caster into the Gray instead of the intended destination. Even the contact other plane spell had a chance of pulling the caster into the Gray.

History
In the late 15 century DR, a book on the history of Athas was part of the collection of the arcanaloth headmaster of the Dweomercore level of Undermountain.

Appearances

 * Adventures
 * Waterdeep: Dungeon of the Mad Mage (mentioned only)