Admittedly I just sort of scanned the article but...
Unless Im missing something these “secret” tunnels are all over the place. The town nearest me has a property where one building along a main business road burned down or was demolished years ago. There was a big steel door apparently installed by the city with padlocks on it. A person could sit at the grocery store behind it and watch the kids go in and out when somebody cut the locks.
Of course they werent actually particularly “secret” as nearly every building down there had a tunnel that led to it. Its just that people often didnt remember why they were there and made up their own stories (around here nearly EVERYTHING is claimed to have something to do with Al Capone).
They were primarily coal delivery tunnels.
This kind of reinforces that must have missed something, I think there was an article some years back about shanghai tunnels beneath LA that turned out to also actually be coal delivery tunnels.
Coal deliveries, leftovers from earlier structures, drainage (if you’re talking about Chicago, they made the river run backwards to build the sewer treatment system), lots of pretty ordinary stuff. 😶
Some of the older homes out here in The Boonies had doors on the second floors. Those dated from the 19th c times when there were no snowplows etc and sometimes it was needed for access to the house in the winters (some big-assed snowfalls back then). Needs vanish and their explanations wind up in the local cemeteries. 👻