You have to watch this
This woman lives in suburbia and has an absolutely bonkers set up to excavate rock etc. She installed ventilation down there. She had a tunnel fire once. I've been following her for a little while. What do her neighbors think is going on? Imagine you buy a house and find a deep ass secret tunnel in the basement? She answers lots of questions in the comments, but she never answers anybody who asks "why."
My favourite comment I saw on one of her videos was something like, "so do we have an objective or are we just expressing ourselves through tunneling?"