The Astral Plane is huge, covering the entire volume enclosed by the Crystal Barrier. The vast majority of this space is unformed, occupied by clouds of diffuse anima and various astral denizens such as radiant dragons and void sharks (as well as their prey, radiant sheep among them). Running throughout are the tubes and pipes of the Great Mechanism, distributing anima to all parts of the Dream.
Within this immense volume of space lie 5 domains--ordered zones inhabited by astral creatures. The Celestial City is centered around Eua; the other four are shaped like sections of a spherical shell with radius equal to that of Quartus's orbit, although together they do not add up to a whole sphere. Scattered through the internal volume are demi-planes, islands of stability in the churning Astral Sea.
The Celestial City
Located at the center of the Astral Plane, contiguous with Eua (the sun) and the source of it's radiance, the Celestial City is the home base of the 1st Host and the center point of the Great Mechanism. It is composed of four separate zones, each with a separate purpose. These four zones are connected by portal networks, although most of the denizens here can fly under their own power.
The Celestial City is at the center of the Dream. As such space is oddly distorted, especially near the World Core. Up and down are strange--no matter your orientation around the parts of the Core, the rest of the city is always above you. The whole city is sheathed in about a mile (from the closest obstruction) of breathable, flyable air (really anima that behaves like air). Once you leave that bubble gravity no longer applies. Within that bubble, things are drawn to the plane of the World Core. If you were to fall, you'd yo-yo back and forth, eventually (slowly) coming to a rest on the level of the Core.
The World Core
About two miles across and one mile wide, the World Core is the heart of the Great Mechanism. Made out of a material that appears to be brass, but is much more resistant to attack, it controls the power that keeps the entire Dream functioning. Two vortexes of anima spiral into the central segment--one from above and one from below. These vortexes glow with a steady light and provide the lighting for the entire Celestial City. Each of the circular structures is actually spherical--like beads strung onto a circular wire. The outer layer of each sphere is uneven--some are filigree, others are covered in gears that occasionally spin and move. The beads are hollow--the laborers that maintain the World Core work and live in them. The rings are gigantic conduits 64 feet in diameter; through them pulse terawatts of power. The entire core revolves slowly around the axis of the vortexes, exactly matching the rotation of Eua itself, revolving once every month.
The central pod is different from the rest--the outer surface is made of overlapping disks set edgewise into the surface of a smaller sphere. Those disks spiral upward and downward--at the very top and bottom are obelisk-like pylons that catch the anima from the vortexes and channel it into the core. Scholars believe that at the center of that pod is the Heart itself with the Divine Four fused into it. Only the Congregation has access, and then only on command.
The closest area of the City to the World Core, the Machinarium holds the forges, production facilities, and workshops of the 4th legion of the 1st Host. A spherical volume covered in buildings and chasms, it is home to the millions of devils belonging to the Territory of Thoraz as well. From here, portals link to the Host's outposts throughout the Dream and to the Elemental Planes of Fire and Earth for each of the planets. It is said that the entire area is one gigantic machine--it is certain that it rearranges itself from time to time.
Home to the research facilities and testing grounds for the 3rd legion of the 1st host, the Laboratorium lies on an oblong disk positioned on a level with the Machinarium but directly on opposite sides of the Core. Very few beings willingly go here--even fewer return.
The Field of Ardor
This is the furthest area of the City from the Core--it is also the largest. A disk 64 miles wide with a hole in it for the central vortex, it is the only part of the city not entirely covered in buildings. The Field houses the Well of Souls (the place of rebirth for the angelic Hosts) as well as the headquarters for the 1st Legion of the 1st Host and the 4th legion of the 4th Host. Newly-reborn angels are trained here and the senior angels have their estates here as well.
Mara--Home of Desiring
A mix of country and city, this domain is covered in greenery and lush vegetation. The second-smallest, it has an area of about 500,000 times that of Quartus. It contains the homes of Sakara, Peor-fala, Aerielara, and Kela-loran. The devil Territory here is that of Mara-deva.
Ghenna--Home of Striving
A harsh land with mighty beasts, Ghenna is dominated by the Grand Arena where heroes, devils, and elemental beings fight for glory. Second in size, it is about 100 million times the surface area of Quartus. It is home to Tor-elan, Roel Kor, Korokonolkom, and the Hollow King. Here is found the Territory of Chou.
Aaru--Home of Knowing
This small domain is covered in workshops, libraries, and laboratories. Smallest of the domains, it occupies an area of only 20,000 times that of Quartus. It is the home of Yogg-magus, Loran Hae, Lon-Ka, and Ytra. It is the Territory of Leiutis.
Naga Padoha--Home of Living and Dying
This vast wilderness of strange plants and animals is the home to Pinwheel, Melara, Selesurala, and Lae-loara. Gigantic seas churning with predators and prey dot the landscape, each many thousands of times the whole surface of Quartus. Where do the Sparks come from for these creatures? No mortal knows; if the Congregation knows, none will tell. The largest of the domains, Naga Padoha is nearly 250 million times the surface area of Quartus. It is also the home to most of the Ascended Heroes and also to the strange beasts that prowl the astral plane. It is the Territory of Ka-Kola.