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Mammoth Cave
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MAMMOTH CAVE Kentucky
Annual Visitors: 400,000
Worst Crowds: Memorial Day to Labor Day (especially between 10 a.m. and 2 p.m.)
Claim to Fame: It’s the world’s longest, most crowd-pleasing cave.

What attracts humans to caves — allegorical or otherwise? Unfortunately, Plato hasn’t returned our calls yet, but we can only assume that there’s something irresistibly primal about entering the jaws of a massive hole in the earth. Especially when it’s Mammoth Cave, the mother ship of subterranean natural wonders.

Now You Know: Visitors have been touring ?Mammoth Cave since 1816.

Mammoth Cave National Park’s featured attraction contains more than 390 miles of mapped and explored passageways, making it the longest known cave on the planet. More than 130 types of animals inhabit this underground geokingdom for at least part of their life cycle, including 14 species of bats alone.

Sounds like plenty of elbow room, right? Not as much for the tourist species. Only 10 miles of the cave are open to the public, and only on guided tours that can fill up with as many as 120 guests on a typical busy day. Even in Mammoth’s gargantuan Rotunda room, or on Broadway (a 40-foot-high, 60-foot-wide passageway that meanders for three miles), that can be a spoiler.

“If you’re here in the summer, especially between 10 a.m. and 2 p.m., the place is just packed with visitors,” says Vickie Carson, the park’s public-information officer.

Unsurprisingly, it’s the opposite in the winter, when central Kentucky isn’t high on most vacation radars, but here’s what you need to know about the cave itself: “It’s the same temperature year-round in there — a wonderful 54 degrees,” Carson says. “In mid-January, it feels almost balmy inside, and you may very well have a tour all to yourself. Walking along Broadway in the ?offseason when you’re practically alone is one of the most surreal, peaceful experiences you could ever imagine.”

Escaping the crowds during the warmer months, when more than a dozen mainly high-capacity tours are offered, will require more drastic measures. Booking an 8:30 a.m. slot, before all the tour buses arrive, is a start. An even surer bet: reserving a spot on Mammoth’s Wild Cave Tour — a 6.5-hour, five-mile hike (and occasional belly crawl) that’s limited to just 14 brave, helmeted souls — gets you into the cave’s deeper innards, where handrails, lights and snack-doling nannies dare not tread. “It’s a great opportunity to experience parts of Mammoth that few see — but it’s not for everyone,” Carson adds. And that’s exactly the point.