This place really needs to lighten up.
The Dark Alleys (細道, Hosomichi, Alleys) is an area accessible through a stone pillar in Floating Stones World.
The Dark Alleys are a series of narrow, poorly-lit alleyways through a block of residential buildings. Various objects line the alleyways, such as wooden fences up against the walls, large stacks of cinder blocks, and planter pots growing flowers and small shrubs.
The illumination in this area can be improved by equipping the Lantern effect, but only marginally so.
Directly to the east of the main entrance, past the first alleyway, is a small room that contains a robot. This robot is holding a monitor with several different display functions (a sine wave, a gray grid of varying intensity, an eye that follows Urotsuki, etc). Some of these displays react to specific effects when they are equipped (most notably the Chainsaw effect).
Navigating through the interconnected alleys will eventually lead you to the Dark Stairs.
The Dark Stairs (石壁, Ishikabe, stone walls) is a series of underground tunnels with grey concrete walls, connected by short sets of stairs leading further underground. Little plants can be seen growing up from the floor of the tunnels, even deep underground. Abstract pieces of graffiti can also be found painted on the walls in certain areas.
As you descend further underground through the tunnels, the area will get progressively darker.
In the deepest parts of the tunnels, the tileset will change to a darker industrial one, with heavily rusted walls and rusty pipes replacing the plants. All the graffiti in this version of the tunnels will appear inverted.
There is a random chance for this to happen in any part of the tunnels, becoming more likely at lower levels.
At the bottom of a long flight of stairs at the very end of the tunnels, there is a pair of paper dolls hanging from the wall that will give you the Teru Teru Bōzu effect if you interact with them to take them down.