Urban spelunkers in Paris: "It's so unexplored that we could run into Xavier Dupont de Ligonnès"

Thomas, a 32-year-old rope access technician, explores the underground tunnels of Paris with friends, disguised as workers. They access a restricted technical gallery where historical pneumatic clock synchronization took place. This system, invented by Victor Popp in the late 19th century, used compressed air to synchronize clocks across the city.