This transmedia experience takes the audience on a journey to discover the treasures hidden beneath the streets of Paris. By turning the city into a playground, the user embarks on a personal adventure at the very heart of the capital. Through a playful and interactive narrative, the audience explores the history and urban transformations of Paris. As they wander through the city, they learn not only to decode their surroundings but also to uncover the inaccessible wonders of the underground—like scars left by time. Using both a book and a mobile application, the user experiences the city’s major transformations through a story unfolding across three key eras: the French Revolution, World War II, and the present day. The various routes offered tell the story while revealing the hidden marvels below, in resonance with the world above. The mobile phone acts as an audio guide, a map, and an interactive window into the city’s underworld. The application automatically activates at each stage when the user is geolocated, delivering both the audio narration and augmented reality images of Paris’s depths. The book serves as a tangible companion to this digital journey—a cultural and historical artifact, a detailed map, and a narrative extension.