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.
If you're into RV life, van life, or camping amongst others, Montana has many excellent RV Parks to choose from. They're vastly different and offer an array of amenities from outdoor pools, playgrounds, seclusion, or creeks that run right through the property.