Check out the Williamson Tunnels:
The Williamson Tunnels are a labyrinth of tunnels and underground caverns under the Edge Hill district of Liverpool in north-west England.
They were built in the first few decades of the 1800s under the control of a retired tobacco merchant called Joseph Williamson.
The purpose of their construction is not known with any certainty. Theories range from pure philanthropy, offering work to the unemployed of the district, to religious extremism, the tunnels being an underground haven from a predicted Armageddon.
Although some of the tunnels have been lost over the years, a lot of them still exist today, under what is now a residential area.
One section of the tunnels has been cleared and renovated and is open to the public. The remaining parts of the labyrinth are closed, with many suspected tunnels yet to be rediscovered.
Friends of Williamson's Tunnels is a voluntary organization which is trying to find and excavate the whole of the system. We are one of the biggest local history societies in Britain.
Much more at the site - fascinating bit of history. Here is a photo from the site - the tunnels are quite extensive. All being excavated by volunteer labor.