London Under: the Secret History Beneath the Streets Reprint edition

In this vividly descriptive short study, Peter Ackroyd tunnels down through the geological layers of London, meeting the creatures that dwell in darkness and excavating the lore and mythology beneath the surface.
 
There is a Bronze Age trackway below the Isle of Dogs, Anglo-Saxon graves rest under St. Pauls, and the monastery of Whitefriars lies beneath Fleet Street. To go under London is to penetrate history, and Ackroyd's book is filled with the stories unique to this underworld: the hydraulic device used to lower bodies into the catacombs in Kensal Green cemetery; the door in the plinth of the statue of Boadicea on Westminster Bridge that leads to a huge tunnel packed with cables for gas, water, and telephone; the sulphurous fumes on the Underground's Metropolitan Line. Highly imaginative and delightfully entertaining, London Under is Ackroyd at his best.