Almost every culture had the idea of an underworld — a shadowy realm where souls traveled after death and faced various challenges. In modern life, we have the Tube — an underground world we physically descend into every day, hidden beneath the surface of the city. It’s like an invisible world, concealed out of sight, yet part of our daily reality. In many cultures, those who entered the underworld could not return (with a few exceptions). Yet, after our journey underground, we return to the visible world. What is this modern underground world like, and what kinds of beings live there? What obstacles, opportunities, and rewards does it offer?