Nexus > Playground > Black Caves (page needed) > Monochrome City
This location can also be reached by the upper grass entrance in the Debug Room in version 0.02.5.
It appears to be a completely desolate Asian city lacking in NPCs, and its name comes from the fact that the entire area is completely devoid of any true colour besides Fluorette herself. You can fix the Broken Sandals here.
A Special Event can be accessed from this world. (Pages needed!)