It could be used to travel between the Shardworlds.
“... a place with a black sky and a strange, small white sun that hung on the horizon ... Flames hovered nearby ... Like the tips of candles floating in the air and moving with the wind ... An endless dark sea, except it wasn't wet. It was made of the small beads, an entire ocean of tiny glass spheres”—Shallan Davar
Geographically it appears to be a reflection of Roshar, with its inland seas corresponding exactly to the shape of the land of Roshar.
Shadesmar can be visited by those with an inherent Soulcasting ability. Entrance to it is granted by beings that Jasnah calls a type of spren. They appear in The Way of Kings to Shallan Davar and Elhokar Kholin, and one of these beings (unofficially called a truthspren) is described by Shallan as
“a figure with a sharp, angular symbol hovering above its collar instead of a head”—Shallan Davar
To be granted entrance to Shadesmar, the person wishing to go there must speak a truth about themselves to the truthspren. Whilst Shallan is in Shadesmar, a voice speaks to her and causes her to Soulcast. It is theorised that this voice belongs to the Cognitive aspect of the goblet she is Soulcasting.
Apparently, you need Stormlight (or alternative source of power) in order to control objects in Shadesmar, as well as for soulcasting. Traveling there without sufficient stormlight is considered to be extremely risky.
This is not the only way of entering Shadesmar. There is a way to access Shadesmar on other worlds, though it is not clear how to do so.
Hoid uses Shadesmar to travel between worlds. The Seventeenth Shard may also use Shadesmar for inter-planetary travel, although this is not confirmed. Hoid's method for traveling there is not yet known, though he uses it to travel from world to world. It is possible other worldhoppers use Shadesmar similarly.
Known Places within Shadesmar
- Shadesmar is just a rough translation of "Cognitive Realm" in the language of whoever first found out about it.
- Shadesmar is the Cognitive Realm
- The Way of Kings interlude I-8
- The Way of Kings chapter 45
- The Way of Kings chapter 70
- Does Hoid use Shadesmar to world-hop?
- Written on Puck's copy of Elantris
|Shards||Cultivation · Devotion · Dominion · Endowment · Honor · Odium · Preservation · Ruin · Bavadin's Shard · Survival Shard|
|Shardworlds||Ashyn · Braize · Nalthis · Roshar · Scadrial · Sel · Taldain · Threnody · Yolen|
|Terms||Adonalsium · Sliver · Splinter · Realmatic Theory · Intent · Focus · Investiture · Shardpool · Spiritweb|
|Other||Hoid · Seventeenth Shard · Chronology · Shattering · Worldhopping · Letters|