These captivating pictures reveal the hidden postal railway network that operated below the streets of Birmingham for decades.
The eerie 400m-long tunnel was used by Royal Mail workers to transport deliveries between a sorting office and New Street Station.
It was built in 1970 so electric trucks could lug cages full of letters and parcels from trains, before ferrying them to the office to be sorted.
The office, which is now The Mailbox, was the largest building of its kind in Britain.
The post was then loaded onto so-called 'electric tractors' which carried the mail along the tunnel to the train station.
The rail mail system shuttled post around the city for decades but closed in 1998 when the sorting office moved to Aston.
The tunnel, which doesn't appear on any maps, has been opened to the public for the first time with a series of limited guided tours.
A ballot for the first guided tour attracted 1,500 applicants to fill just 30 places.