When Geraldo opened "Al Capone's Secret Vault" live on TV, I was watching it with my Dad.
My Dad watched the build up to the opening and said "That's just a trash tunnel".
I asked him what that was, and he explained that in the 20s and 30s, there wasn't regular trash pickup, so some businesses just dug long tunnels in their basement, dumped trash in, and when it was full, walled it off.
And that's exactly what it turned out to be.