This excellent tube map reveals the hidden secrets of London

We all know about the many magnificent monuments that you can see from the street-level of London. And most of us scurry about its underground arteries via the tube every day. But many of you won't be aware that there exists a whole other hidden London, buried way down below the capital's mean streets.

Clapham South's wartime tunnel network, for example, was recently opened up to the public for the first time in seventy years, but that's just one example of a hidden treasure lying beneath the surface. The map below, designed by Discover Britain, reveals the existence of underground rivers, a post office railway, the sewer network and other deep level bomb shelters.

It uses the Northern line route as a guide (as well as revealing some facts about current and lost stations on that particular line) - take a look below and discover something you never knew about London.