This is a great article all about the tunnels and how they were constructed: https://www.newyorker.com/magazine/2015/08/03/underworld-monte-reel https://www.new

This is a great article all about the tunnels and how they were constructed: https://www.newyorker.com/magazine/2015/08/03/underworld-monte-reel https://www.newyorker.com/magazine/2015/08/03/underworld-mon...