I have a secret tunnel of sorts in my own house.
It leads out of the basement/bomb shelter down a concrete tube (quite large; a person under 6 feet can stand up) to a heavy metal door that opens inward and then a set of stairs and essentially a set of metal storm doors well beyond the barn, probably 50 yards that can’t be opened from the outside.
Not particularly concealed, although it looks like an entrance to a root cellar or something.
The basement is huge and has tons of fluorescent lights and water.
My assumption is this was a “grow room” for marijuna. Or it could have just been an alternative exit if the house was destroyed.
Wow, what a find! Most modern tunnels (and probably the old ones as well) were built for some important purpose (like the steam tunnel system that heats the Michigan State U campus) and are not particularly decorative, but still interesting.
I crossed the entire campus west-to-east, and a good bit of the north-south distance, completely underground one night with some D and D masterminds. We weren't the first, there was student graffiti down there in spots.
My crappy GPA remains a mystery.
I heard of a guy that had a tunnel like this on his property. He built it as a gun range!