Nobody knew that London has an underground railway system that was hidden from the world's view for decades or even centuries. It took only a few daredevils in 2011 to discover one of the world's most marvelous finds of the century.

According to CNN, a group of youngsters called Consolidation Crew aims to "explore everything" by "place hacking" or literally trespassing private properties, and they decided to go underground. What they discovered was something that has been hiding under the noses of the local authorities. It all started when they found a mysteriously steep spiral staircase that no one knew went. The staircase led them to a series of small man-made tunnels they have hoped to discover something interesting.

In their search, they found a hidden underground railway network known as the "mail train." This underground railway network was formed in the 1920s and was used mainly by the British Post Office. The network ran from 1927 to 2003 and had the world's first-ever driverless electric train which delivered post through and from London. According to historical records, the train ran for 22 hours every day for 365 days a year, with only a two-hour maintenance schedule daily.  

The criss-cross of tunnels not only served as a railway system. It also served as a storage for national art treasures from various art institutions around London. It was noted that during the First World War, paintings and other artifacts were secretly hidden away in the tunnels.

It has been reported that even those people who actually worked in the British Post Office did not know the existence of the speedy railway system underground. It was only the maintenance people who actually know the twists and turns of the network. Nowadays, the discovered underground railway system has been turned into a tourist attraction.