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Despite being explored for nearly 200 years, Mammoth Cave National Park in Kentucky still contains some mysteries.

A team of researchers recently discovered eight previously unknown miles of underground passages in Mammoth Cave, the world's longest known cave system. Led by nonprofit , the discovery expands the total of explored passages within the cave to 420 miles.

"When it comes to discoveries in Mammoth Cave, there truly is no end in sight!" the National Park Service (NPS) tweeted.

Each year, volunteers from the Cave Research Foundation visit the park to map newly discovered passages to locate potential research sites and assist with park management, according to the NPS. It's a complicated process that sees volunteers from the cartographic program trek through the dark and abstract subterranean landscape using compasses, measuring tapes and range finders to reveal new passages.

New caves are continually being discovered and while visitors won't be able to access the new passageways, there are still plenty of routes to enjoy in the five-level cave system, including the Grand Avenue route which recently underwent a major upgrade with new benches and handrails and improved trail paths.

Mammoth Cave, a UNESCO World Heritage Site, is located about 90 miles from both Louisville, Kentucky, and Nashville, Tennessee. It's open year-round to visitors through organized tours. Due to the pandemic, face masks are required to visit Mammoth Cave. For more information, or to book a tour, see .

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