These 5 manmade holes have proven themselves to be testaments to the human will and skill of engineering, all in all making up over 10 miles of deep excavation. Lucky for us here in the United States, Montana and Utah feature two entries on the list—and you may not expect them.
These 5 manmade holes have proven themselves to be testaments to the human will and skill of engineering, all in all making up over 10 miles of deep excavation. Lucky for us here in the United States, Montana and Utah feature two entries on the list—and you may not expect them.