The Mindscape is home to the hero known on Earth as Sleepwalker. In fact, the being that inhabits the mind of Rick Sheridan is but one of a race of Sleepwalkers, sworn to defend the minds of sentient beings from threats originating in the Mindscape. The Mindscape can be used essentially as a doorway into the mind of any sentient creature in existance, making threats from the plane particularly dangerous.
It has been theorized that the Mindscape is where beings minds go when they dream. If this is true, then the Mindscapes connection to other "dreamscapes", such as Nightmare's Dream Dimension.