Young resident Steve Watkins once walked a passageway between the Young High School and Young TAFE campus.
He's certain he's not the only person to have walked the tunnel linking the old courthouse and old jail, and he's calling for people to share what they know.
Between the late 1800s and early 1900s, the tunnel would have been used to transfer prisoners from the jail to the courtroom.
Mr Watkins said the passage is about one-and-a-half metres wide and more than two metres high. He walked it with a hand torch in 1992, gaining access from the old courthouse.
"I guarantee you it's there," he said.
Heritage expert and president of the Young Community and Residents Association, Joe Kinsela, said tunnels under the Young High School have been rumoured for a long time.
"We didn't have definite knowledge of the thing, until Steve described it. All my life in Young people have said 'did you know there was a passage down to the jail?'"
Mr Kinsela, who has a Master's degree in Heritage Conservation, has applied for an interim heritage order so investigations are carried out to establish the exact route of the tunnel, and that no-one working on the site is in danger of falling into the cavity.
"This could be a tourist attraction for Young. I don't know of another one like it," he said.
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