With more than 50,000 caves within the U.S., there’s a mysterious and intriguing world to explore beneath the surface. Natural caverns reveal spectacular geologic formations like you’ll never see on the surface.

For some, the prospect of venturing underground is exhilarating. For others it is frightening.

But as noted author and mythologist Joseph Campbell once wrote, “The cave you fear to enter holds the treasure you seek.” So strike your best Indiana Jones pose — and let’s go spelunking!

In reality, you needn’t fear for your safety while exploring any of the several dozen caves open to public visitation across the country. All of them must adhere to rigorous safety regulations, and most are lighted, temperate and well ventilated.

In most cases, your subterranean adventure will be led and narrated by expert tour guides who consider your well-being and enjoyment as job one.

Sturdy walking shoes (read: no flip-flops or high heels) are a must and a light jacket is suggested since cave temperatures range from 55 to 65 degrees.

So here’s our list — and your ticket — to getting to know America beneath the surface:

Luray Caverns, Virginia

Tucked away below the Blue Ridge Mountains in Virginia’s Shenandoah Valley, Luray is the most visited cave system in the Eastern United States.

It is home to a winding series of large well-lighted rooms with paved floors that feature some spectacular limestone formations and crystal-clear pools. Most impressive are Saracen’s Tent, a 10-story-high column with a rock configuration that resembles folded ribbons; Giant’s Hall, with its towering columns, and Tatiana’s Veil, an intricate composition of crystallized calcite.

But the real star of the show here is the aptly named Great Stalacpipe Organ. It is said to be the largest musical instrument in the world — using electronically controlled rubber mallets to gently tap the cave’s stalactites — creating mesmerizing gong-like tones.

www.luraycaverns.com, 888-443-6551

Mammoth Cave National Park, once described as a “grand, gloomy and peculiar place.”

Mammoth Cave, Kentucky

A national park and UNESCO World Heritage Site, Mammoth is the longest cave system in the world, with more than 400 miles of passageways.

Located in the Green River Valley of south-central Kentucky, it is a subterranean wonderland of vast chambers, glistening pools, travertine dams and complex limestone labyrinths that are at the same time beautiful and eerie.

Early guide Stephen Bishop described the cave as a “grand, gloomy and peculiar place.” A variety of self-guided and ranger-led tours ranging from 90 minutes to six hours are available year-round, but guided tours sell out quickly so purchase tickets online in advance to avoid disappointment.

Tip: the Domes and Drips tour is the favorite of most visitors.

www.nps.gov/maca, 270-758-2180

Meramec Caverns, Missouri

Home to more than 6,000 surveyed caves, Missouri is known as the Cave State — and Meramec is the largest and most visited of them all.

Located along historic Route 66 about 60 miles west of St. Louis, Meramec features some amazing and colorful limestone formations and some interesting history — serving in the 1870s as a hideout for the infamous outlaw Jesse James.

It does, however, suffer a bit from over-commercialization, including man-made props and a tacky sound and light show. One not-to-be-missed natural feature — the Wine Table — is a six-foot-high onyx formation that resembles a three-legged table adorned with grape-like clusters called botryoids.

It was composed millions of years ago — entirely underwater. Guided 90-minute walking tours run every half-hour starting at 9:00 a.m.

www.americascave.com, 800-676-6105

Natural Bridge Caverns near San Antonio, Texas

Natural Bridge Caverns, Texas

Named for a natural limestone slab bridge at the entrance, these caverns, located 30 minutes north of San Antonio, are the largest and most visited in Texas.

Formed by an underground river many thousands of years ago, Natural Bridge features multiple layers of compacted limestone and a wide range of cave formations — stalagmites, stalactites, flowstones, chandeliers and soda straws — and stunning chambers some 200 feet below the surface such as Castle of the White Giants and the Hall of the Mountain King.

Visitors can join several guided tours including the Bracken Bat Flight Tour for an up-close view of Bracken Cave, home to the world’s largest bat colony.

www.naturalbridgecaverns.com, 210-651-6101

Wind Cave, South Dakota

So named for the whistling wind ever present at its natural entrance, Wind Cave, located near Hot Springs, was the world’s first cave to be designated a national park back in 1903.

Considered one of the longest (163 miles) and most complex caves on the planet, it is home to 95 percent of the world’s known accumulation of a delicate honeycomb-like cave formation known as boxwork – formed from calcium deposits as a byproduct of limestone water erosion.

Visitors can explore this fascinating cave through a variety of ranger-led tours including two specialty tours: the Candelight Cave Tour and a more daring and strenuous Wild Cave Tour.

www.nps.gov/wica, 605-745-4600

Carlsbad Caverns, the most well-known of any cavecomplex in the United States.

Carlsbad Caverns, New Mexico

Without question, Carlsbad is America’s most famous cave complex. Since opening to the public in 1924 it has recorded more than 44 million visits and currently entertains nearly a half-million visitors a year.

This labyrinth of more than 120 known caves nestled beneath the Chihuahuan Desert in southern New Mexico was formed when sulfuric acid dissolved the surrounding limestone in a process that began more than 250 million years ago.

Both self-guided and ranger-guided tours are available. Most popular are two self-guided tours that are included in the entrance fee and can be conveniently combined. The first is the 1.25-mile Natural Entrance Trail, a steep asphalt switchback route that winds down 750 feet into the Big Room — a huge 8.2-acre limestone chamber that ranks as the largest accessible cave chamber in North America.

From there, another 1.25-mile path circulates through the Big Room allowing visitors to explore its many spectacular limestone formations. A variety of ranger-guided tours, available at extra cost and only through advance reservations, explore other regions of the caverns.

More than 400,000 Mexican free-tail bats inhabit Carlsbad and they put on quite a show when they whirl out the cave at sunset to feed. From May to October — before the bats migrate south for the winter — visitors can attend a special ranger program at the outdoor Bat Flight Amphitheater (free with park admission) to witness this striking exodus.

www.nps.gov/cave, 575-785-2232

Kartchner Caverns, Arizona

These beautiful caverns, located near Benson in southeastern Arizona, have existed for at least 50,000 years but weren’t discovered until 1974 and it wasn’t until 1999 that they opened to the public as a state park.

The site’s 2.4 miles of passageways lead to two major features — the Rotunda/Throne Room and the Big Room — which can be visited only on separate, hour-long guided tours.

The Throne Room contains the world’s longest known calcite soda straw stalactites and a towering 58-foot-high dripstone column named Kubla Khan.

The Big Room is notable — to speleologists (cave experts) at least — as home to the world’s most extensive formation of brushite moonmilk, a creamy form of limestone precipitate. The Big Room is closed from April 15 to October 15 because it is a nursery roost for more than 1,000 resident cave bats.

A drawback here — no video or photography is permitted.

www.azstateparks.com/kartchner/cave, 520-586-2283