Take a walk into the forest. Trees thick enough to block the sun overhead, bugs you can't identify scurrying to flee your feet, and you're suddenly subdued group of fellow explorers create a palpable sense of anticipation. Your guides crack jokes about lawsuits and heart conditions, at which you chuckle good-naturedly, but you are starting to wonder what you've gotten yourself into.

Fast forward: you enter a clearing. There, surreal in its incongruity, is a gray metal door embedded in the side of a hill. Your guides divide you into small groups, and soon the first group disappears behind the door, into the earth itself. When it's your turn, you follow the line through the frame and down a set of narrow metal stairs that end in another closed gray door several yards below. Side to side, you can touch both walls at once. You look up, and on the ceiling just above your head you find a thick carpet of impossibly oversized crickets. Before you can process that discovery, the door you came in slams shut and the tiny passageway is swallowed in blackness.

Time to panic?

No! You are in one of the safest places in the planet: with a tour group. The adventure is the Frozen Niagara Tour offered by Mammoth Cave National Park. The jungle is an extension of the nearly 53,000 acres the park spans. The metal door is the entrance to the cave itself - the natural entrance collapsed years ago - and the narrow hallway is an airlock, as it's important to the integrity of the cave's ecosystems to keep its internal pressure as close to its natural state at all times as possible. The giant crickets? Those are really giant crickets, or 'cave spiders', and they are part of the cave environment. Once the second door opens, the tour begins.

Mammoth Cave, located just outside of Cave City, Kentucky, is the most extensive cave system in the world. Although 350-plus miles of the underground maze have been explored and mapped, no one really knows just how vast the system is. The park services offer tours throughout several parts of the cave, covering a wide range of skill/fitness levels, tastes, and prices. For instance, the Mammoth Cave Discovery Tour is self-guided, lasts about half an hour at an easy walk, and covers less than a mile for $4; at the other end of the spectrum, there's the Wild Cave Tour, which lasts more than six hours, covers more than 5 miles, poses challenges like extended crawls through areas as little as 9 inches high and free-climbing cave walls, and costs $46 (helmets, kneepads, and lights are provided). Check the Cave Tour page for specific information on the 13 tours and for their schedules.

The Frozen Niagara Tour is one of the most crowded that visitors to Mammoth Cave can take, but when it's one of the biggest vacation days of the summer and you haven't made reservations, you can't be too picky. Tours can and do sell out, so it's a good idea to call ahead. FN is a two hour, ¾ mile, non-physically taxing jaunt into the tunnels, domes, and pits of a small section of the cave; there are a lot of stairs to go down in the beginning, and the cave atmosphere in general is not for the claustrophobic, but it is, in general, a great way to be introduced to the cave system. Although the group was large, the guides' initial creation of small groups goes a long way toward making it less crowded, as each group actually enters the cave at a different pace.

The first thing that hits a lot of people, once the second metal door is behind them, is the chill. Even though it may be scorching outside, the cave system's natural temperature is 54 degrees. That it's cold underground may seem like common sense, but it often catches visitors off guard. Most guided tours will make sure to include a healthy dose of historical information, too, so be prepared to learn the difference between stalactites and stalagmites if you don't already know.

We didn't see much wildlife beyond the cave spiders; of course, if I were a cave-dwelling animal, I would probably stay off the lighted, tourist soaked path, too. What we did see, though, was two hours' worth of exquisite beauty. It was enough even to block out the inane comments of fellow tourists ("Wow, this cave is really big." "Yeah, it's mammoth.") and use up all the film in my camera within twenty minutes or so; the pits appeared bottomless and the domes seemed endless, we were treated with dry cave passageways as well as wet, old and new, huge open spaces and tight fits. The tour guide was enthusiastic and witty, and although the whole experience would have been enhanced by the absence of some particularly obnoxious tourists, it was well worth the $11.

It would take weeks to explore all the natural beauty of the park. There are more than 73 miles of trails to walk, bike, or ride on horseback, and if animal watching is a pastime of yours, you'll enjoy the flocks of wild turkey, myriad white-tailed deer and great blue herons, along with several endangered species including freshwater mussels. There are sinkholes scattered throughout the park, and fishing for more than 100 species of fish in the Green and Nolin Rivers is good all year. Ask about regulations at the visitor's center. One of the best things about walking the park is the wide variety of plant life; you'll see everything from witch hazel to bloodroot to the elusive hairy buttercup. Score one for the Midwest and its temperate climate!

There are a million things to do at Mammoth Cave National Park besides take tours of the cave, but the labyrinth underground is not to be missed. At the rate human interaction seems to be spoiling the public parts of the cave - by far the most disheartening part of the tour was the climactic Frozen Niagara room, in which few delicate stalagmites remained intact, as most tips were broken and stolen - it might not remain public forever. Regardless of the future or the past, Mammoth Cave is definitely a national treasure. I view the sheer volume and intensity of the cave system as one more excuse to cheer, 'Bravo, Mother Nature' in the Midwest.

Questions?
If you want more information about this area you can email the author or check out our North America Insiders page.