Hi All,
An good idea for someone would be to go down into the cellar of The Old Ship (If there is one) with Ground-Penetrating-Radar (GPR) and see what's buried down there if any. It would show on the GPR that there's a 20ft gap then a hollow tunnel. The Operator can differentiate the difference between a pipe and a hand-dug tunnel. With permission from the owners you could drill down and have a look to see where it goes.
Thanks,
Regent3