1. Mammoth Cave – Kentucky Established as a national park in 1941 and honored as a UNESCO World Heritage Site in 1981, Mammoth Cave boasts the longest known cave system in the world.

An area of Lincoln National Forest known for a complex cave system was protected from oil and gas drilling and other mineral extraction, with the block on development extending for 20 years. The ...

More: Forest Service seeks 20-year block on oil and gas in cave system They can also be sent via mail to 333 Broadway Blvd. SE, Albuquerque, New Mexico, 87102.

Wind Cave is among the longest known cave systems in the world, but unlike most massive caves, it isn't spread out over a long distance. Instead, it descends deep down into the earth.