Alright, so Shadowfell in DnD is an alternate plane of reality that mirrors the mortal plane (The normal world), it is a dark, desolate place full of decay, it lacks both color and light and can be described as black and white with light black and dark black, light sources can be seen from much much further away, gravity and time are the same, it is a dark twisted reflection of the mortal plane that distorts what building or landmarks might exist
Shadowfell Wiki page
Shadowfell Wiki page