![Explorers add 8 miles to world's longest known cave system](https://ic-cdn.flipboard.com/futurecdn.net/d5f0f8c233fa1a8b4ffdb0efa3ab166b331f0c3f/_xlarge.jpeg)
Mammoth Cave National Park has set a new record. The world's longest known cave system just set a new record after surveyors spent hours mapping an …
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