The Umbral Realms, also known as the Plane of Shadow or the Shadowfell, were an "echo" of the Material Realm exhausted of magic and devoid of emotion. All sensations, both sensory and emotional, were lessened for any creatures on the plane, and its landscape was a desolate place full of decay. The plane lacked light, and and all things looked as if the colour had leeched out, leaving nothing but dim black or white.
As it ran parallel to the Prime Material, its geography was similar although not entirely identical to that of the Material, but the natural landscape could markedly change. Upon entering the Plane of Shadow, the local features were usually quite similar, but diverged rapidly away from the familiar the further an interloper traveled, eventually breaking into the Deepmists. Due to the ever-changing geography, the Plane of Shadow was subject to relatively frequent but very small earthquakes referred to as "shadow quakes". Similarly, time did not flow at the same rate depending on the place; lost time could suddenly "catch up" to a mortal, sending them into fits of exhaustion or hunger, or even killing them instantly if many years had passed.
It was considered the effective opposite of the Vivid Realms in the Cosmic Wheel cosmology.