22 Unforgettable Adventures in National Parks Across America

16. Exploring an Underground World in Mammoth Cave National Park, Kentucky

Beneath the rolling hills of Kentucky, a vast, hidden world awaits. Mammoth Cave National Park is home to the longest cave system on Earth, with over 400 miles of explored tunnels—and counting. Unlike traditional hikes, exploring Mammoth Cave takes you into a labyrinth of winding passages, massive underground chambers, and eerie subterranean rivers. Guided tours range from easy, well-lit walks to intense, crawl-through spelunking adventures. For first-time visitors, the Historic Tour takes you through key highlights like Fat Man’s Misery, a narrow passageway that twists and turns through the limestone. If you’re feeling adventurous, the Wild Cave Tour is an adrenaline-pumping experience that involves squeezing through tight crevices, crawling through tunnels, and rappelling into darkness. Beyond its geological wonders, Mammoth Cave has a rich human history, with evidence of Native American use dating back over 5,000 years. Explorers have mapped its depths for centuries, uncovering ancient artifacts and mysterious petroglyphs. The cave’s cool, constant temperature (54°F year-round) makes it a perfect escape from the summer heat. Whether you're fascinated by geology, history, or adventure, Mammoth Cave offers an underground journey like no other.