The Nightmare Lands is a supplement that details the mist-covered Nightmare Lands on the borders of Demiplane of Dread in the Ravenloft setting. In this netherworld the Nightmare Court searches for dreamers to trap them in "dreamscapes" which amplify where their secret feelings to unbearable levels so that the Court can feed on their fears. These dreamers are subjected to this mental assault nightly and soon go insane unless the Nightmare torturer is defeated.^[1]

The Nightmare Lands includes four books: "Book One: Journal of Doctor Illhousen", "Book Two: Rules of Dreams and Nightmares", "Book Three: Book of Nightmares" and the "Monstrous Supplement".^[1] The "Journal of Doctor Illhousen" explains Nightmare adventures to the players, and how characters can reach the Nightmare Lands - physically and as dream beings - to aid victims held by the Nightmare Court. The journal also notes the reality shifting nature of this world.^[1] The "Rules of Dreams and Nightmares" details the complexities involved in Nightmare adventures, as well as how characters can build their Mental Fortitude, or self-confidence in their "dreamself", by facing their worst nightmares which gives them the strength to break free of the influence of the Court.^[1] The "Book of Nightmares" and "Monstrous Supplement" can be combined together for an adventure scenario for characters in the Nightmare Lands