In a deserted station some 65ft below the streets of London, England, engineer Ray Middlesworth turns his great brass key and the Post Office Underground Railway roars into life.
The sound of the 1920s locomotive engine bounces off the peeling century-old brickwork as we rattle along the two-gauge track.
The mysterious world of subterranean London, looks set to give up one of its secrets next year as a previously hidden underground railroad opens to the public.
The Mail Rail is a 23-mile network once used by the UK’s Royal Mail postal service to transport letters and parcels beneath the city.
Its small electric engines entered service in 1927, shuttling between eight main sorting depots. It closed 11 years ago.
A section of the system will reopen as a visitor attraction in early 2017.