Shadesmar is a plane of existence. It is the cognitive realm and binds the other two realms of existence (spiritual and physical) together.
Shadesmar can be visited by those with an inherent Soulcasting ability, or those who have a Soulcasting fabrial. So far the only known characters to travel there are Shallan Davar and Jasnah Kholin, though it is likely that Hoid has been there as well.
Most people only interact with Shadesmar subconsciously through intuition or artistic expression, but Shadesmar is all around everyone all the time. It is created by the deep, profound thoughts of people and then shaped by spren.
Lay of the landEdit
Geographically, it appears to be a reflection of Roshar, with its inland seas corresponding exactly to the shape of the land of Roshar. Within it are:
Shallan describes Shadesmar as an endless sea of tiny black beads that appear to be made of glass. There, the sky is black and a small white sun above the horizon seems as though it is not far away. Above the sea of beads, flames hover 'like the tips of candles floating in the air and moving in the wind'.