https://www.pcgamer.com/dark-souls-mod-plunges-the-entire-game-into-darkness/

Dark Souls' Tomb of the Giants is one of Lordran's most treacherous environments. With only the player's immediate vicinity lit, the area is mostly pitch black—save for the faint glow of the Demon Ruins lava beneath. Notaprofi's Pure Darkness mod applies the same effect to the entire game.

And it looks bloody terrifying. Look at these screens: