Dowsing the Walbrook is an interactive audiovisual installation that uncovers London's buried Walbrook river as a spectral force - unseen, yet influencing the city from beneath. The work reinterprets the traditional practice of dowsing, once used for water divination, as a contemporary digital interaction, inviting participants to explore the boundaries between the urban surface and the hidden subterranean currents. Flowing historically through the Roman Temple of Mithras beneath today's Bloomberg building near Cannon Street, the Walbrook symbolised a liminal passage between physical and spiritual planes for Mithras worshippers. Though now hidden beneath the city's surface, channelled through subterranean sewer systems, its presence persists as a ghostly current within London's urban subconscious. No longer visible as water, the Walbrook instead surfaces in street names, road layouts, and subtle contours of the urban landscape, reflecting the Mithraic duality and presenting an enduring dialogue between above and below, physical and spiritual, past and present. In the installation, participants explore an audiovisual environment through hand gestures captured by a sensor, engaging in a digital form of dowsing. Their movements transform audiovisual elements, shifting from clear documentary references into abstract, sensorial wash. In this reconfiguring, the Walbrook emerges as a spectral presence, reminding visitors of London's deep-rooted connections to unseen currents. In collaboration with sound artist Jamie Turner.