Avalon, the Realm of Faerie

Technically speaking, Avalon is a particular place within the greater realm of Faerie, but it is the one with the strongest connection to Earth and best known to its superhuman inhabitants, so it has come into common use as another name for the fey realm.
Faerie is home to shape-shifting magical beings with powers of illusion known collectively as the Fae and called by numerous names in human folk legends, such as the Gentry, the Good Folk, and the Dwellers Under the Hill. Because of their mercurial nature, it’s difficult to describe the Fae as a “species.” There are numerous types, each with their own particular proclivities and specialties. The only real things they share in common are: an innately magical nature, a curiosity about the material world, a general lack of imagination and innovation, and a related devotion to tradition to the point of influencing their physical nature.
While often capable of changing their form and influencing the form and appearance of other things, the Fae lack creativity and imagination. Their forms and illusions are aped from things they have seen and experienced in the physical world, and once the Fae adopt something, they become strongly attached to it. This makes their culture baroquely complex and littered with superstitions and ancient geasa, or “bonds,” traditions so strong it causes the Fae physical pain and harm to violate them. Among these include keeping their sworn word and various vulnerabilities, particularly to iron, which is anathema to many faeries.
Once, the realm of Faerie was strongly connected to Earth, particularly in the British Isles and parts of Europe. Fae interaction with humanity waned following the downfall of King Arthur’s Camelot. The folk of Avalon took the fallen king with them into their realm to heal and await the day when he would be needed once more, while Faerie gifts like the sword Excalibur were also returned. In times since, Fae incursions to Earth have been rare, with the exception of Thomas Rhymer's visit to Faerie.
The inhabitants of Avalon have remained largely the same since the Middle Ages, and most of their realm seems like a fantastic version of Earth during that time, although some parts are even stranger. Some of the Fae have at least a passing acquaintance with modern human customs and technology, even if they do not always understand either.

Type

Dimensional plane