Interesting. There should be some artifacts or writings down there to indicate uses. Or so I’d think.
Possibly. But as I just noted to another poster, I believe St. Louis has an old underground area that's been revitalized. It could well be that the city built new construction on top of old. Unusual, but possible.
A lot of cities/towns developed “undergrounds” during prohibition. The honky tonks were in the basements, and elaborate tunnel systems connected them and connected to escape routes in the event of raids.