Far Realm, resulting in the abominations known as starspawn. Natural humanoids tainted by the Far Realm are known as foulspawn. The Far Realm is occasionally referred to as "Outside", because it seems to exist outside of reality as defined by the world, the fundamental planes and the parallel planes. In Eberron, the Far Realm is equated with Xoriat, the Realm of Madness. Other fictional interpretations Within the context of the game, there are many theories of the organization of the planes. For instance, in some lands it is believed that there are multiple Prime Material planes, rather than one containing all the worlds or planets. In these lands the Ethereal planes are believed to surround each Prime Material plane. Additionally, other Dungeons & Dragons cosmologies were developed after Greyhawk for various other campaign settings, however, "they would be subsumed under 5e's umbrella concept of the multiverse". Dark Sun cosmology One of the hallmarks of the Dark Sun setting was Athas' cosmological isolation, something that broke with the rest of the canonical Dungeons & Dragons universe. Many of Dark Sun's AD&D contemporaries are accessible via planar travel or spelljamming, but Athas, with very few exceptions, is entirely cut off from the rest of the universe. While it retains its connections to the Inner Planes, access to the Transitive Planes and Outer Planes is nearly impossible. The reason for the cosmological isolation is never fully explained. Eberron cosmology The Eberron cosmology, used in the original Eberron campaign setting, contained thirteen Outer Planes in 3rd edition, and gained at least two for 4th edition under the new cosmology. They exhibit traits similar to those of the standard D&D cosmology but also some (Irian, Mabar, Fernia, and Risia) appear more like Inner Planes. The cosmology was unique in that the Outer Planes orbited around Eberron through the Astral plane. As they orbited, their overlap with the material plane changed and access to those planes became easier or restricted. Forgotten Realms cosmology The Forgotten Realms cosmology was originally the same as that of a standard Dungeons & Dragons campaign. The cosmology for the 3rd edition of D&D was altered substantially so that it contained twenty-six Outer Planes, arranged in a tree-like structure around the central 'trunk' of the material plane of Toril. Unlike the Outer Planes of the standard D&D cosmology which were heavily alignment-based, the Outer Planes of the Forgotten Realms cosmology were faith-based.