Negative Energy plane

The Negative Energy plane, sometimes called the Plane of Death or the Negative Material plane, was an Inner Plane or Energy Plane of the Great Wheel cosmology and the World Tree cosmology models. After the Spellplague, the Negative Energy Plane collapsed into the Elemental Chaos, mixing with all the other Inner Planes. The goddess Shar managed to channel some of this death energy into the Plane of Shadow and create the Shadowfell. Cosmologists believe that Negative Energy and its opposite Positive Energy, combined with the four elements, make up the known universe. This plane was extremely hostile to all forms of life and energy. Only the undead could travel with impunity here, and the more powerful undead could harness this death energy to attack the living with devastating effect.

Cosmology
According to the Great Wheel cosmology model, the Negative Energy plane could be reached via the Ethereal Plane or an adjacent elemental plane, but not by an elemental vortex. (However, there is speculation that the Void card in the deck of many things brought a person here.) If traveling through the Deep Ethereal, a pure black curtain of vaporous color indicated the boundary of the Plane of Death's Border Ethereal region. Such was the influence of the Negative Energy plane that the boundary with the Border Ethereal was weak and fluctuated randomly at times. Travelers thinking they were safe staying in the Border Ethereal could suddenly be dumped on the Plane of Death some distance from the rapidly receding border. Using the spherical model, this plane was adjacent to the quasi-elemental planes of Dust, Ash, Vacuum, and Salt. Temporary gates could be created by the plane shift spell.

As described by the World Tree cosmology model, the Astral Plane connected all planes with the Prime Material Plane and the Ethereal Plane was only used for journeying between locations on the Prime. The Negative Energy plane was not connected or coterminous with any other elemental plane. The spell astral projection could be used to reach the Negative Energy plane via a cold ebony color pool. Additionally, the gate and plane shift spells could be used to open a temporary portal to this plane.

Description
"It is the blackest night. It is the heart of darkness. It is the hunger that devours souls."

- Manual of the Planes

Both cosmological models described this plane as being an airless, featureless void of darkness with gravity being an individual choice. Somewhat paradoxically, both models also allow that structures existed on a landscape of sorts, either made of the physical, solid darkness, or perhaps of elemental earth that could survive in regions of the plane (called doldrums) that did not exhibit the major-negative dominance trait. The atmosphere was not vacuum but could not be used by winged creatures for propulsion, nor could it sustain life, yet torches and lanterns would burn for a short while before being extinguished. Magical light sources worked as usual but visibility was extremely limited. These characteristics lead cosmologists to speculate that it is the energy-sucking nature of the plane that greedily devoured any life-giving energies rather than the complete lack thereof, but the difference is of interest only to sages. In practical terms, without protection from the negative energy and elimination of the need to breathe, death was only a few minutes away at best.