EIGHT additional miles of Kentucky's Mammoth Cave are uncovered that extends the 10-million-year-old structure to at least 420 miles long | WHAT REALLY HAPPENED X-Frame-Options: DENY X-Frame-Options: SAMEORIGIN

EIGHT additional miles of Kentucky's Mammoth Cave are uncovered that extends the 10-million-year-old structure to at least 420 miles long

Kentucky's Mammoth Cave is the longest in the world and an additional eight miles of passages have recently been discovered, bringing the cave to at least 420 miles long.

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