A tunnel rumored in urban legends to appear regardless of time or place—while walking normally or inside a dream—leading to a mysterious world once passed through. Beyond the tunnel, one is said to arrive in deserted spaces such as skyscrapers growing from the sky, cities composed entirely of ruins, or empty shopping malls. The space that appears often aligns with the desires of the person who entered. However, the common thread is a near-total absence of human presence. Generally, once the person who entered is satisfied or a certain amount of time has passed, if they wish to return, an exit tunnel will reappear, allowing them to go back.