A tunnel rumored like an urban legend. It is said to appear regardless of time or place—while walking normally or within a dream—and leads to a mysterious world once passed through. Upon exiting the tunnel, one might arrive at uninhabited spaces such as skyscrapers growing from the sky, cities consisting only of ruins, or deserted shopping malls. The spaces that appear often align with the desires of the person who entered. However, the common thread is the near-total absence of human presence. Generally, once the person who entered is satisfied or a certain amount of time has passed, an exit tunnel will reappear if they wish to return, allowing them to go back. On very rare occasions, humans may appear. In such cases, they become obsessed with the person who entered the tunnel and will do various things to make that person never want to leave the space.