Located at the exact center of the universe[1], the planet Eternia is a unique receptacle of powerful energies where magic is relatively commonplace and in which fantastic creatures and people with remarkable abilities abound.
Eternia is a terrestrial planet covered in vast oceans and continents with diverse biomes, ranging from the perilous Vine Jungle and Tar Swamp, to the peaceful Evergreen Forest, to the vast desert known as the Sands of Time, and to the northern Ice Mountains. It seems to be orbited by numerous moons. Its atmosphere and gravity are similar enough to Earth's to allow natives of one planet to survive comfortably on the other and vice-versa. The same is also true of Eternia's sister planet, Etheria.
The Sea of Eternity, located amidst the Mystic Mountains, feeds a large river that supplies water to both the Evergreen Forest and the Vine Jungle. The combined vegetation of these two habitats is largely responsible for providing oxygen to the atmosphere of Eternia, which humans and other animals need to survive.[2]
Unlike Earth, Eternia is divided in a light hemisphere and a dark hemisphere; the latter of which being where the dreaded Snake Mountain is located. While the light hemisphere is ruled by King Randor's government from the capital city of Eternos, the dark hemisphere is the domain of Skeletor and his Evil Warriors who seek domination of the entire world, and indeed the entire universe.
Containing the source of the planet's magic is Castle Grayskull, where the Sorceress resides to protect the secrets of this ancestral fortress. Surrounded by a bottomless pit, the castle provides a link to the actual center of the planet and therefore the universe. At the core of Eternia lies the so-called Star Seed: a fragment from the universe's creation that can grant infinite power to anyone who holds it.
Advanced civilizations have flourished on Eternia since ancient ages, and although centuries of war and conflicts have caused the planet to mostly regress to a more medieval-like state, remnants of advanced science abound in the form of aircraft, artificial intelligences, energy-based weaponry and others. Additionally, the strong magic present on the planet occasionally provides means to travel between worlds and even between dimensions.
Perhaps as a result of its long history, the presence of interplanetary and interdimensional gates, and invasions by off-world conquerors such as the Horde; Eternia is now home to a surprisingly diverse array of sapient races, as well as an impressive biodiversity of fauna and flora.