In our real universe, there are little spheres of earth called planets which circle large sources of light called stars in a vast space of air so attenuated as to be a near perfect vacuum. In Ever-Earth the order of the elements is different. Here there are large pockets of air centered about small sources of light in a universe of endless solid matter. The air bubbles seem to often be vast spheres, anywhere from one to a hundred miles across, burned out of the earth by their central stars, which hang and glow of their own accord.
Gravity
The physics of Ever-Earth is rather different from that of the real world on the larger scale, but surprisingly similar - seemingly identical -= in the small scale. Gravity, for example, has a universal "down" in the same direction everywhere. It affects greater masses less than smaller ones. The tiniest of insects may be observed to be somewhat sturdier than their real-world counterparts, while great giant bats do not need such crippling support as makes them rare in the real world. This is why Ever-Earth is not crushed under its own weight; being infinitely huge, the bedrock and major mineral formations do not bear down on the areas below them. Only the loose material in a cavern's ceiling will weigh down, so cave-ins need not be as disastrous as they would be in the real world with such vast spaces.
Stars
The "stars" in Ever-Earth vary. Some are as bright as our sun, while others cast glimmer like a moonless night. They are as varied in colour and special properties as they are in size ands intensity. Some exude great heat, while others create a region of intense cold around them. In some cases, one flying or otherwise approaching such a star will discover that it is a purely non-physical phenomenon; one can fly right through. If one had the means to suspend it, a palace built here would be filled with and seem to exude light. In other cases, it will be discovered to be a vast and unalterable, immovable crystal.
The pockets of air range in size, most being 1 to 10 miles in diameter while others may be hundreds of miles across. The air in these varies, some being dry and desert-like while others filled with steaming billows as about a mineral spring. There are pockets filled with strange fogs and other pockets filled not with air but with other materials altogether, water, fresh or salt being but the most mundane of examples.
Some "foam regions" seem to be nearly half bubble, but these seem no more in danger of collapsing than the rest of this solid universe.
Veins
Woven through the mass of Ever-Earth are veins. Some, veins of metal or coal or peat (formed from geo-plankton) or other minerals are solid and still. Others, veins of water or quicksilver or magma, are liquid and flowing. There are as many rivers of magma as there are of water, salt or fresh. The magma is self-heating; as long as it can flow it will stay hot, and the faster it flows the hotter it gets. A magma sea, being sluggish in its currents, is likely to be relatively cool. Similarly, there are streams of air, or, to be more precise, particular gas mixes, which flow ever upwards. All of these seem to operate on the alchemical principle of "like attracts like," for wherever such as stream is found, even if artificially diverted there, springs will appear along its course to feed it. It is speculated that all physical matter is composed of mixtures of the "divine elements" and so may exude, under the proper influence, any other material.
Ever-Earth is apparently infinite in extent. Legends tell of journeyers who have spent entire lifetimes traveling either up or down or in a compass-guided direction for entire lifetimes without reaching even a rumor of boundary. Some speculate that, while the distances must be hundreds of thousands of miles, if not millions of miles, it is possible that Ever-Earth is "looped," such that whatever direction one went, one would eventually return to where one started. Such speculations are highly unlikely; more likely, Ever-Earth is indeed infinite in all directions.
Tales of "surface worlds" are known in a tiny fraction of Ever-Earth cultures. These are generally dismissed as imaginary "fairytale lands" made up to amuse the simple-minded or to illustrate moral points. Obviously, "surface worlds" are actually just giant bubbles.
A stranger claiming to be from a "surface world" would obviously be either insane, if he or she sincerely believed this preposterous claim, or insulting if trying to perpetrate such an obviously preposterous claim. In a few places access to "the surface" is a known fact. Any such "surface" is not the surface of Ever-Earth. Rather, is seems that in many other universes, the deepest complexes of caverns have natural Gates or Portals establishing permanent contact between these strange other universes and Ever-Earth. These may be single points of contact, perhaps artificial, or "plains of contiguousness," broad areas through which any tunnel or burrow will pass from the one universe to the other. The passage may be marked by some phenomenon, such as a sheet of shimmering dark and a cold tingling, or it may be totally imperceptible. It seems likely that such connections only intersect air-filled tunnels by happenstance, and more commonly link the nerves of metallic ore or living lava veins of the multiverse's many manifestations of the trans-universal Earth.
Life in Ever-Earth has only subterranean ancestry; nothing here is derived from surface forms. It is probably more varied than life on the (alleged) "surface worlds" because local populations are more likely to be relatively isolated and thus likely to evolve their own variations.