Hobby Tunneling

Hobby tunneling is tunnel construction pursued as a pastime rather than for any practical or commercial purpose. Hobbyists typically dig by hand with minimal equipment, and some devote years or even decades to a single project. In a number of documented cases these tunnels were dug in secret and were only discovered by other people by accident once the digging was already well under way. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/