The Great Tunnel connects the two halves of the divided by the Autumn River. Ground was broken on it September 25, 1774 and completed eleven years later. Its construction claimed the lives of hundreds of workers.

During its heyday, it accommodated more than six thousand people an hour and inspired many songs including the music halls favorites, "Don't Leave Me in the Tunnel" and "My Love is a Tunnel Digging Man." Today the Great Tunnel is now longer used. Instead it is a World Heritage Site for the Mole People and a nature preserve for several species of eyeless salamander.