One of my hobbies (I have many,) involves railroad history. This is commonly called “railfanning” in the US and “trainspotting” in the UK. Railfans have great interest in trains and the infrastructure that supports them. I’m very lucky to live in a part of the USA where trains are very common and continue to play a role in the average citizen’s daily life. Where I grew up in North Carolina, one only saw freight or the occasional Amtrak passenger train.
That said, I was surprised to learn today that Chicago had an extensive network of underground freight tunnels dating back to 1906. If you’re interested in industrial history, this is certainly worth your time. I’ve always had an interesting fascination with steam and mechanical tunnels (and regret not having taken a summer job in maintenance of such when I was younger,) and these were a treat to read about.