Neth, the Plane That Lives, is a fictive demiplane in the Dungeons & Dragons Planescape setting. It is a living, sentient plane of finite size that has an immense curiosity. Neth learns of other planes by absorbing the flesh of visitors and then incorporating their memories into itself. Neth’s most important goal is to learn the reason for its own existence.
The only access Neth has to the rest of the multiverse is through a single metallic, peach-colored pool on the Astral Plane. Those who look into the pool from the Astral Plane might notice a huge eye flash into focus on its surface, which quickly fades.
Sometimes, Neth will choose to encapsulate its visitors. Two folds of membrane will come together and ensnare and seal off the victims. Neth will then flood the compartment with either preservative or absorptive fluid. The preservative fluid will put the victim in temporal stasis, and the victim can be revived if the fluid is drained away. If the compartment is flooded with absorptive fluid, the victim will dissolve and be absorbed into Neth itself, including the victim’s memories.
Neth is living membrane the size of a continent. It is folded upon itself and resembles an enormous paper ball with a radius of about twenty-five miles. The spaces between the membrane’s folds can be a hand’s span across or larger than a city. The spaces are filled with air-saturated fluid, but visitors can still breathe in them. If the plane were spread flat, it would be about five hundred miles in diameter, and the average thickness would be approximately thirty feet.
Air- and water-breathing visitors to Neth can breathe and speak in Neth’s fluid normally. If they swim around unnoticed, they might see organ buds larger than city blocks, beings behind membranous capsules, and the humanoid antibodies of Neth mindlessly going about their business. Every part of the living demiplane has a soft, pink glow. Neth can also flush the fluid wherever it wants, carrying visitors along with it, usually to the Visage Wall to be questioned.
Gravity on Neth is the same strength as that on the material world; however, Neth chooses the direction of gravity’s pull and may change it at will. Time is normal on Neth. Neth can move its interior membrane at will, creating or destroying fluid-filled spaces.
The only thing native to Neth is the plane itself. Neth creates humanoid subunits of itself called Neth’s Children, sometimes for specific short-term purposes before reabsorbing them.
Neth's Children are usually identical to flesh golems and resemble a vaguely humanoid mass of flesh. Though they are free-moving, Neth’s Children react to stimuli according to the preprogrammed will of Neth. Sometimes, Neth creates his children to serve as antibodies, but they are more often sent to other planes, instructed by Neth to explore and return for reabsorption, thus giving Neth more knowledge.
On Neth, the portal to the Astral Plane appears as a twenty-foot-wide mouth-like cavity, which Neth can open and close at will.
At Neth’s center is a thick knot of membrane at least a mile across where all the folds come together. This serves as Neth’s brain. Other parts of the membrane also serve specific functions, which include areas where the membrane can be easily deformed for communication, encapsulation, and budding Neth’s Children.
The Visage Wall is an area of Neth's membrane where Neth communicates with visitors. It contains thousands of head-shaped bumps that resemble the likenesses of those previously absorbed by Neth. Neth speaks to its visitors from about five or six of the heads simultaneously, questioning them in order to learn more of the outside world.