(CNN)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.
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London's hidden underground mail rail to open to visitors
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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, including Paddington in the west and Liverpool Street in the east.
The line, a miniature version of the city's own Underground public transport system, closed 11 years ago when some depots were shuttered and sold off.
Now it's been announced that a section of the line will reopen as a visitor attraction in early 2017.
Much of the line has changed little since its closure, with old engines and equipment sitting parked in stations.
In recent years, mail workers have operated subterranean trips for young children at Christmas, painting festive murals on tunnel walls.
When it opens to the public, the remaining trains will be converted to allow visitors to take a short ride beneath the Mount Pleasant Post Office in the city's Clerkenwell district.