Shadowfell

It is the toxic plane of darkness and power.
It is the hidden place that hates the light.
It is the frontier of powers unknown.

 

The mirror of the Feywild

It exists as sort of counterpart to the Feywild, in the sense that it was a reflection, or "echo", of the Prime Material plane. Unlike the Feywild, it was a bleak, desolate place full of decay and death.  

Description

The most striking and immediate impression a visitor to the Plane of Shadow experienced was the lack of color and light; no sun, moon, or stars adorned the vault of the inky black sky, and all things looked as if the color had leeched out, leaving nothing but black and white.
  Due to the ever-changing landscape, the Plane of Shadow was subject to relatively frequent but very small earthquakes (called shadow quakes) that resembled an earthquake spell in an area about two hundred feet (sixty meters) in diameter. For those on the ground, damage was equivalent to a Prime earthquake, but shadow quakes could also disrupt the shadow walk spell and dump unfortunate travelers onto the Shadowfell in the middle of the disturbance at a place very likely unknown and far from their destination.