From 1927 to 2003, Royal Mail in London had its own Underground rail system, dubbed "Mail Rail".
The line ran from the Paddington Head Sorting Office to the Eastern Head District Sorting Office in Whitechapel.
It operated 19 hours per day for 286 days per year and carried around 4 million letters a day.
You can now visit the museum and ride the train, check out. www.postalmuseum.org
