Monsieur Chapeau

The current edition of the council magazine "Medway News" reports that with the aid of a £154,000 grant, a team of one professional and several volunteer archivists are for the next three years to catalogue 500 boxes of the Rochester City archives dating from 1227 (yes, 1227) to 1974.

If there are records of tunnels under Rochester, that is quite a likely place to find them.