The Shadow Realm is one of many names given to a strange plane or dimension similar to the natural world. It exists alongside the natural world, and is mostly a place of darkness and despair.
The Shadow Realm seems to be the place that the souls of the dead travel through before achieving their final rest or reward, whatever that might be. Thus it is a place of drifting souls and undead spirits. Non-the-less, there are living beings that seem to happy to call the Shadow Realm home. The Shadar-Kai are one such race, building a society in many ways similar to those of humans in the natural world. The best example of Shadar-Kai society would be the city of Umbrer
There are many places where the barrier between the realms is thin; a person knowing how to find such a place, or even an unwary traveller, can easily find him or herself in the Shadow Realm. One such place is located on the Isle of Lost Dreams, or, as it is known in the Shadow Realm, the Isle of Lost Souls. Perhaps it is the association of the Shadow Realm with death that means most of these places correspond to areas of death such as cemeteries.
Explorers of the Shadow Realm report that there are many correspondences between the Realms, however, it is dangerous to expect too close a similarity. One thing is known for sure; time moves differently between the realms. There is many a tale of a hapless scholar searching old ruins who wanders accidently into the Shadow Realm. There they are able to research first hand the myths and legends, often culled from the lips of those that made them, but on their return to the natural world the years catch up and the scholar is reduced to a pile of grave dust..
That said, there are those who trade between the realms, as ‘shadow goods’ as they are called, fetch a good price in the natural world or the Fey Realm. Some even use the Shadow Realm simply as a short cut, as the differences in physical geography can result in many miles.
The gloomy nature of the Shadow Realm can have an effect on the spirits of visitors from other realms, and even residents find their moods darkened. Apathy and lethargy are common, and the Shadar-Kai can go to extremes to fight this. Visitors should be prepared for extremes of emotions while within the Shadow Realm.
Unlike the natural world, there is little trade between settlements. The Shadar-Kai can produce most of their needs close to hand; large settlements spread around places of ritual or political significance, not along trade routes, and travel across the Shadow Realm’s dark landscape is much less frequent than in the natural realms.