Beneath Britain's cities and coastline lies a second, hidden landscape of caves, catacombs, and tunnels, and this survey moves from one to the next. Edinburgh's underground city, sealed off after cholera and fire, gets explored as a warren of vaults once packed with the poor. The Hell Fire Caves, carved into the Chiltern Hills for a secret eighteenth-century club, come with their own rumors of ritual and scandal. Liverpool's tunnels, dug on the orders of the reclusive Joseph Williamson for reasons nobody fully agreed on even at the time, run beneath streets that show no trace of them from above. Brighton's Victorian sewers, still functioning brickwork from the 1870s, reveal how a seaside resort quietly solved its waste problem underground. Coastal coves and caves along the smuggling routes round out the picture, showing how contraband moved inland while customs men searched the wrong places. Each stop treats the tunnels as physical evidence of the history built to stay out of sight.