The Dreamscape (or Dream Realm) is the dream space parallel to the real world. Its cosmogony traces back to the Forgotten God, formerly the Dream God.
Canonical Origin
The Dream Realm was the personal domain of the Dream God before his fall. When the god was shattered into seven fragments birthing the Seven Daemons, his domain shattered too. What remains — fragmentary, contradictory, peopled with nightmares — is the Dream Realm Awakened explore.
Persistent Geography
Despite its dreamlike nature, the Dream Realm contains lasting places: - Forgotten Shore — first shore of the Nightmares - Tomb of Ariel — key sanctuary of the Doom War - Citadel of Hope — fortress of the Demon of Desire - Great River — vast river crossed in Vol 7 - Underworld — Nether's domain - Mantle — deep layer of the Dreamscape - The Cradle — origin or womb of the Dream Realm
Connection to the Spell
The Nightmare Spell is the instrument by which the Dream Realm keeps pulling mortals in — perhaps an unconscious attempt by the broken Forgotten God to recover his integrity.