Shadowfell

A plane of existence adjacent to the Prime Material Plane, a bleak, desolate place full of decay and death, drained of color and emotion, full of sorrow and loss. The dark reflection of the Prime Material, just as the Feywild is its bright reflection.

The landscape of the Shadowfell is a dark, twisted echo of what existed on the Prime. Upon entering the Plane of Shadow, the local features are usually quite similar: entering from a forest put you in a shadow forest; entering from under water put you in a similar body of water, etc. But from that starting point, the landscape diverges rapidly away from the familiar, and on subsequent visits from the same starting point it diverged in different ways, making mapping the Shadowfell a useless endeavor.

Landmarks are usually recognizable but altered in some bizarre way: buildings might be constructed in a different style, built with different materials, at a different location, and usually in a dilapidated condition or otherwise strange and distorted. Similar sites were sometimes called "shadow-analogues".