grandfather was an engineer

You could go check public records. I don't know much about whether or not it is legal for you to see his tax records, my guess would be that you could considering that you are his next to kin or are close to next of kin whoever it would be. I think tax records would indicate employment history,

I assume these are the old delivery tunnels built around 1900. Small electric trains rode on a narrow gage track in the tunnel. There are a number of books written about these tunnels. I am sure you track down such books with Google. The tunnels were built to supply downtown stores and offices with supplies such as heating coal, while not impacting the heavy downtown surface traffic. They are now used as utility conduits.

Not too long ago, in the 80's or 90's, a company driving pylons in along the river drove one through the roof of a tunnel flooding most of the downtown area that was below river level. To prevent the entire tunnel system and building basements from being flooded due to a single breach, flood gates were installed in the tunnels.

A short segment of the "Blues Brother" movie was filmed in the tunnel (where Carrie Fischer is confronting John Belushi). You can see in that film that the tunnels were not very big. I read somewhere that the concrete the tunnels are made is holding up well and the tunnels should last for a long time. Being near the lake, at the level of the tunnels, the ground is probably all saturated sand.

Of course Chicago also has underground rapid transit tunnels and the Deep Tunnel (for flood control). The subway came along much later than the delivery tunnels and the Deep Tunnel was built in the 70's and 80's.

The Chicago Water Tower is a major city landmark. It is about the only structure that survived the great fire of the 1870's. It is a stand pipe surounded by a castle like facade, that was used to control water pressure in the pumping system.