Maybe this is a construction barrier factory.
The Abandoned Factory (廃工場, Hai Kōjō) is an area accessible from the Forest Pier by way of the boat.
When first entering from the Forest Pier, the area is a bit dark (It's gradually more darker), silent, and desolate, consisting of a waterway lined by strange fungus-like growths. Following the water, Urotsuki will pass by a poster depicting an abstract prohibition sign, a broken window, and a round sculpture similar to those found in the Forest Pier being overtaken by foliage.
The second area has industrial music and is filled with large and small pipes and some fungi. At the end of this area is a dimly lit doorway that connects to the next area.
The hallway between the second and third area is barren except for windows lining the wall and a metal grate at the end, which Urotsuki can step onto out of the boat. The third area consists of metal ladders and staircases, with the occasional fungus growing in some places. At the leftmost side of the area is a bench, which Urotsuki can sit on.
The very bottom of the area is filled with shallow water, construction barriers, and four numbered archways, out of which only the first and third are accessible. The first archway leads to an alleyway lined with locked doors, a neon sign, and one last unlocked door to the far right which leads to the Arc de Pillar World . If you walk up to the fourth archway, a white creature with a large eye can be seen standing beyond the barriers.
Through the third archway there's an area which consists of several smaller culverts with railed conveyor systems overhead. To the right are a large amount of fungi in an unreachable room. Continuing on, there is a room with graffiti resembling a flower or butterfly on the wall, and a ladder to the northeast and south.
The southern ladder leads to a floating door, which turns out to be a black and red head with a stray left eye in a dark hallway. This hallway is under construction, blocked on both sides by traffic cones. An odd creature wades around in the water here that reacts to the marginal effect.
The northern ladder leads to another waterlogged hallway with more culverts, fungi, and construction barriers, the latter of which is likely an indicator of upcoming content in future versions of the game. The room winds down past more culverts, eventually coming to a crossroads with two culverts, marked by some cones to the left.
The culvert on the right can be chainsawed open, leading out to an unfinished area featuring a strange cottage on a small island. The island is surrounded by giant white flowers, which sway in the wind; a rusted mailbox stands out front, which makes a sound when interacted with.
A ladder has been placed across the water to use as a bridge, but is currently blocked by an insidious traffic cone. There is nothing else of interest here aside from a flashing cube that slowly moves around the bottom of this area, which will take you back to the flooded hallway when interacted with.
Continuing further down the path leads into a new section with a metal grated ceiling, more graffiti visble on the leftmost wall, and more of the prohibition signs, exiting to a sewer with a blob-like creature wading through it. Continuing onward leads to Urotsuki suddenly getting eaten by a large red monster (Similar to Yume Nikki's Big Red) that will take her to the Wind Tunnel.