Olivia Solon, writing for Wired:
The Post Office Underground Railway — AKA the Mail Rail — was the world’s first driverless electric railway. It launched in 1927 and was used to transport tonnes of post from one side of London to another, with stops at large railway hubs such as Liverpool Street and Paddington Station, where post could be collected and offloaded for transportation around the rest of the country.
The service continued to operate until 2003, when it was closed down — it had become much cheaper to transport mail by road.
Since then, the trains and the tunnels have remained in place, but plans are afoot to turn part of the network into this public ride as part of plans to build a new National Postal Museum, which have just been approved by Islington Council.