Includes index.

Look down. What's under your feet? We all live on the crust of our planet, a layer as thin as the shell of an egg - so what's below you? Perhaps the fossilised bones of a velociraptor that died exactly where your sofa is now? Or an Anglo-Saxon burial ship, weighted with gold treasure? Or a deep limestone cave, home to a scuttling eyeless creatures that were once thought to be dragons? Or a maze of underground tunnels where people are watching a movie or dancing to loud music you can't even hear? Get digging