There are secret tunnels along the entire length of the Kansas Turnpike that most drivers don't know exist. These bunkers and tunnels could also be lifesavers.
They're not for public use and behind locked doors, but for those that can use them, the little-known Depression-era tunnels under Grand Rapids, Michigan come in handy when it gets super cold.
Tunnels under San Angelo, Texas, were thought to be just legends until someone broke through a basement wall during construction opening up a lost world.