The Seven Spheres is a worldbuilding project loosely based on ttrpgs like DND (especially spelljammer and planescape) and Pathfinder, alongside things like Elden Ring and other such worlds. It's generally fairly dark fantasy, with healthy smatterings of steam and dieselpunk and a lot of cosmic horror.
What are the Seven Spheres?
The Seven Spheres is the name given by in-universe scholars to the seven major regions of existence that make up the known universe. The Spheres are all believed to either be infinite, or so large that measuring them is impossible. The Spheres are home to a variety of familar and unfamilar life, and each display markedly different laws of physics to our own world. Broadly, the cosmology is split into the Inner Spheres (The Cage and the Crucible), and the Outer Spheres (The Sanguine, Astral and Empyreal Spheres, alongside the Foundry and the Terminus) The Seven Spheres are each detailed briefly below.
The Crucible
The closest of the Spheres to our own reality, the Crucible is so named for being a 'mix' of the different traits of the other spheres, and for being the main source of energy in the cycle of souls. The Crucible is made up of hundreds of galaxies, stars and planets, and a great many alien and familiar species call it home. (In dnd terms, this is the Material Plane. In real world terms, this is the real world.)
The Cage
Made up of the four philosophical elements, and the points where two or more combine, the Cage gets its name for the belief that it was placed around the Crucible by the gods to prevent mortals from entering the Outer Spheres. If this is the case, it has profoundly failed, as mortal life has spread across both the Cage itself, and the Spheres that lie beyond it. The Cage is regarded as being extremely hostile to life, with mortals only capable of surviving in regions containign some level of the mixtures of the elements (with pockets of air being unsurprisingly essential). However, the Cage also hosts a wide variety of natives, such as Elementals and stranger creatures who have adapted to its harsh environments.
The Sanguine Sphere
The Sanguine Sphere is a place of instinct and emotion, ruled by the innate desires of mortalkind. Often called the sphere of the body, the is named for its outer edge (if an infinite sphere could physically have one), which is known as the Sea of Blood, or the Acheron. Nothing dies permanently in most of the Sphere, meaning it is perpetually locked in an endless war fought practically merely for the sake of fighting. A variety of creatures call the Sanguine Sphere home, such as the infamous Devils, ancient Asuras, and the powerful Valkyries.
The Astral Sphere
Said to be the Sphere of the mind, the Astral Sphere is the home and birthplace of the majority of gods, and is defined by the great silver void known as the Argent Sea which makes up the majority of its structure. The Astral Sphere is believed to be a reflection of mortal consciuousness, and as such is especially mutable for strong minds. Although less war-torn than the Sanguine Sphere, the Astral Sphere is still a dangerous place, being home to the unpredictable fey, living thoughts known as the Vesh Hikal, and many planar migrants, such as the Cthil and the Sahnou elves.
The Empyreal Sphere
Home to the underworlds of Mortalkind, the Empyreal Sphere is believed to hang on the edge of the Terminus, and is perhaps the least-travelled of the Spheres. It is an empty black void, punctuated only by the occasional underworld and titanic petrified corpse. It is home to the Demons of the Nadir, alongside the Archons, said to be the last witnesses of the universe's creators. Alongside this, the Empyreal Sphere is home to the Necropolis, the point of judgement for mortal souls, and as such contains many of that realm's guardians, the Usubians.
The Terminus
The Terminus is the end of all souls, sometimes called Creation's Maw, and the mother of oblivion. The Terminus is like a vast black hole, and represents the end point of the planar tide known as the River Styx. Once a soul has experienced their true death in their afterlife, they are drawn here, where there energy is broken down into its base components and then drawn back into the Terminus' opposite, the Foundry. Very few creatures dwell within the Terminus, as it is the anathema to life itself. However, a few Usubians safeguard the Sphere, and the eldest of the Qlippoths dwell within, seemingly unaffected by pure death that surrounds them.
The Foundry
The source of energy flowing back into the Crucible, the Foundry is, ironically, just as dangerous as the Terminus to most forms of life. It is surrounded by a great sea of plant life enervated purely by its power, but entering it results in immediate healing, then cancerous growth, then swift death as a being is quite literally healed to death. Despite this, a few souls survive on this plane, with the Etaidra guarding its outer edge and the death-souled Yal Hevra dwelling in its blinding depths.
Annddd thats all for this post! Asssuming I can count, that should be seven! Expect more to come from these in future, as I have more than enough on the Sanguine Sphere to keep going for a good while, and the others should get sporadic posts as well!