Planes of Power
The Ethereal Plane
The Ethereal is often likened to an ocean, but rather than water it is a sea of boundless possibility. It consists of two parts: the Border Ethereal which connects to the Inner and Prime Material planes, and the Deep Ethereal plane which acts as the incubator to many potential demiplanes and other proto-magical realms. From the Border Ethereal, a traveler can see a misty greyscale version of the plane from which they are traveling.
Some sages believe that each plane is only connected to its own Border Ethereal, which means inter-planar travel necessitates entering the Deep Ethereal and then exiting into the destination plane’s own Border Ethereal plane. Others liken the Border Ethereal to a beach, i.e. a place where the land (prime) meets the sea (Ethereal). In those cases, the border Ethereal is more like a shore and a Prime is like a seaport. Sages point to Spelljamming travelers as proof of this theory.
Unlike the Astral Plane, in which solid objects can exist (though are extremely rare) anything and everything that goes to the Ethereal Plane becomes Ethereal. It should be noted that while there are theories (like the Ether Cyclone) that there are places which connect the Ethereal plane to the Astral Plane, no theory has ever been proven. That said, portals and gates from the Ethereal & Inner planes to the Astral and Outer Planes do exist (and they often baffle sages).
The Ethereal is littered with demiplanes, some of which are large and well-known to Planar travelers. The most well known are Faerie (oft called the Feywild), the Plane of Shadow (sometimes called the Shadowfell), the Plane of Time (if you can find it!), the plane of Dreams, and the Demiplane of Dread (which players know as Ravenloft). Most demiplanes are found in the Deep Ethereal. In fact, most demiplanes are born here, and many fade back into nothingness here.
Finally, one periodically hears talk of a demiplane called “The Far Realm”; whether this alien place is a demiplane, a conduit to an alternate reality, or some demented prime material world is not known as so few sages have ever traveled there and survived to formulate their theories.