Blood World (血生臭, Chinamagusa, Bloodiness) is a somewhat small area accessible from the rainbow door in the Stone Maze.
Blood World is a dark scrolling area filled with pools of blood, scattered razor blades and white ghosts crying blood. You can return to the Stone Maze by traveling northeast of the entrance and interacting with the red sign/hammer there. North of this is a pool of blood that may contain another red sign that leads to the Intestines Maze, but this is not guaranteed. (There is a roughly 26% chance it will be present)
If you enter the center of the largest pool of blood, you'll be teleported in a horizontally looped lake of blood with many crying ghosts, a bloody pedestal surrounded by knives, and a towering white creature rooted into a darker pond of blood at the very north. Using the Chainsaw effect on the white creature will prompt it to let out a loud groan. The area darkens, the music changes, and the ghosts will swarm around you and attempt to inhibit your motion while Scary Faces pursue you. If they catch you, the screen fades to black, and Urotsuki wakes up. (Viewing this minor event will unlock a wallpaper)
It is possible to escape from the Scary Faces and get away with your assault unharmed. The ghosts are slow enough that if you bike away with the Motorbike effect, and you should be able to find a razor blade at the south of the lake that will teleport you back outside. Outside, there will be more Scary Faces that will continue to pursue you, and the exit back to the Stone Maze will be surrounded by more Scary Faces. If you can time yourself interacting with the hammer so that none of the Scary Faces surrounding it touch you while you do it, all without getting caught by any of the other Scary Faces, you will be teleported back to the Stone Maze where it is safe.