Cosmic World (Cosmic) is an area reachable from the Old Train Station.
Cosmic World is an area immediately recognizable for its strange and garish colors, causing it to stand out compared to the surrounding worlds and other works of its developer. The islands form a massive archipelago that is notoriously difficult to navigate due to the cluttered objects and lack of visual clarity. Two unreachable NPCs and a nearly invisible Vending Machine can be found here.
You start off from the balcony of a building with a stairwell leading down. East of the entrance (accessible by travelling in a spiral) is a dark blue building which leads to a dark room with bones attached to the walls, a bench and a lamppost, and a rainbow flower on the ground. Stepping on said flower and facing the wall, you can chainsaw it making purple "blood" splatter. Interacting with the box near the bench will show three kanji written in an old-fashioned style. The text is most likely 「白昼夢」 (daydream). After using the box it's possible to see the text by accessing one of the books in the lower section of the Library, the one from the second bookshelf on the left. By travelling south from this building and eventually east before you hit a particularly narrow patch of island, you can find a forest area with another brown rusty building in the center. This building leads to the Square Ruins.
Using the Marginal effect here will make the world turned darker and gray-scale. In addition, howling with the Wolf will make the ground flash faster, and lighting up with the Haniwa will make the ground flash much faster.
Nexus → Red Streetlight World → Gray Road → Grass World → Green Neon World → Construction Frame Building → Cog Maze → Forest Pier → Abandoned Factory → Arc de Pillar World → Mansion → Deserted Pier → Deserted Town → Chaotic Buildings → Transmission Tower World → Complex → Old Train Station → Cosmic World