Helpers dig out other 'Mersey tunnels'.
Around 40 volunteers from Liverpool spent the weekend uncovering a section of tunnel in Edge Hill built by wealthy 19th-century philanthropist Joseph Williamson.
Williamson paid hundreds of Merseyside soldiers returning from the Napoleonic Wars to build a seemingly pointless maze of tunnels as a way of keeping them employed.
The volunteers helped The Friends of Williamson's Tunnels map and dig a part of the tunnel system that had remained untouched since the 1800s.
A visitor centre with a restaurant and bar, plus a museum, is being developed at the main entrance of the tunnels in Smithdown Lane and is due to open in the summer.
Duncan Roberts was one of around 40 volunteers with youth development charity Raleigh International.
The 20-year-old from Aigburth said: "I have been amazed by what I have seen.
"I wanted to help and see what was going on for myself.
"Don't get me wrong, I like staying in bed on a Saturday morning, but it's nice occasionally to change your routine and do something that is historically interesting and worthwhile."
Williamson Tunnels centre manager, Hilary Travis, explained:
"The project to open up the tunnels will bring back to Liverpool parts of its heritage and be a magnificent tourist attraction. The big triple tunnel that cuts through the railway cutting is about 30 feet under the courtyard and an impressive feat of engineering.
"And the tunnels will create jobs again for tour guides, and restaurant and bar staff.
"We don't know where all the tunnels lead - that's part of their excitement and appeal.
"But we wouldn't have got this far without the help of the Friends of Williamson group."