Nightmare Lights are light sources found within the Ruins. They cannot be opened or destroyed with a Hammer. Instead, the amount of light they emit depends on the current state of the Nightmare Cycle that the Ruins are in; the more extreme the magical state, the more the Nightmare Lights open up.

Nightmare Lights drain the player's sanity when they are open and if the player is near. The actual magnitude of the drain depends on how much light is coming from the Nightmare Lights (how "open" they are). During the Warning phase they will drain 10 sanity/min, while in the Nightmare phase they will drain 15.



Shadow Creatures will appear around the lights, even if the player is not insane. The Shadow Creatures only appear during the Nightmare phase and are hostile to the player. Once the Nightmare Cycle is completely over, the creatures will die, dropping Nightmare Fuel in the process.

The lights are fueled by Nightmare Fuel that extracted from unknown depths below. This is a major example of the excessive use of Nightmare Fuel by the Ancients that led to their downfall.