Nightmare is a malevolent dreamworld that is home to the sinister Nightmarens including its creator Wizeman the Wicked, and a location in the NiGHTS universe. This place within the Night Dimension where visitors go when having bad dreams.
NiGHTS reaches Nightmare when they take on a Nightmaren boss. Nightmare is reachable in the Dream Gate by falling in the strange dark ocean or being captured and taken by Wizeman into his dark kingdom. If a Visitor falls into the dark ocean and Wizeman himself manages to steal their Ideya, they will become doomed to be within Nightmare in their sleep forever.
- Wizeman the Wicked - Creator of the Nightmare realm, well-known Level 1 Nightmaren, and lord of nightmares.
- Reala - A first level Nightmaren and loyal right-hand minion of Wizeman.
- NiGHTS - Former Nightmaren turned Nightopian and hero of the Night Dimension.
- Bomamba - An ugly feline witch and a Level 2 Nightmaren.
- Cerberus the Hellhound - A ferocious canine beast and a second level Nightmaren.
- Chamelan - A crafty chameleon magician and a Level 2 Nightmaren.
- Clawz - A fiendish feline creature and a second level Nightmaren.
- Donbalon - A laughing clown and a Level 2 Nightmaren.
- Gillwing - A monstrous tadpole-like dragon and a second level Nightmaren.
- Girania - A giant gladiator-themed piranha and a Level 2 Nightmaren.
- Gulpo - A giant hungry piranha and a second level Nightmaren.
- Jackle - A maniacal jester and a Level 2 Nightmaren.
- Puffy - A giant rabbit-like opera songstress and a second level Nightmaren.
- Queen Bella - A giant spider queen and a Level 2 Nightmaren.
- It is sometimes called the "Nightmare World".