For decades, London's mail was routed around town via an underground railroad of sorts:
Officially known as the London Post Office Railway, the 6.5-mile-long system opened in 1927. Its purpose was to transport letters and parcels to sorting and delivery stations across the city, from Whitechapel in the east to Paddington in the west.
Operating between 19 and 22 hours a day, the Mail Rail chugged back and forth using driverless trains, never having to worry about getting stuck in the traffic that clogged the roads above.
But a funny thing happened by 2003: it became cheaper to transport the mail by trucks than to continue using their little electric trains. It seems odd, because we're always told how effective rail systems are, yet petrol-powered trucks eventually won out, and the system was mothballed. Now, they're planning to convert the tiny trains to hold passengers, with plans to reopen the facilities as a museum within five years.