CARLSBAD, NM — SUMMER 1898 — As Jim White told and re-told the tale, he was just a teenager when, towards evening, he rode his horse past a hole in the ground and saw a small volcano. Tying his horse to a tree, Jim approached. What he thought was smoke turned out to be bats. Thousands and thousands of bats.

"I found myself gazing into the biggest and blackest hole I had ever seen, out of which the bats seemed literally to boil." Well, Jim figured, “any hole in the ground which could house such a gigantic army of bats must be a whale of a big cave.”

After waiting a half hour for the bat eruption to end, Jim slipped through the hole and entered “a darkness so absolutely black it seemed a solid.” Creeping “cat-like” across ledges, Jim spent an hour underground. Days later, when he returned, he brought a ladder, a lantern, and a ball of string to help find his way out. And down he went.

For three days, Jim explored “rooms filled with colossal wonders in gleaming onyx. Suspended from the ceilings were mammoth chandeliers-clusters of stalactites in every size and color. Walls that were frozen cascades of glittering flowstone, jutting rocks that held suspended long, slender formations. . .”

A century ago this week, when President Calvin Coolidge made the site a national monument, Americans began exploring Carlsbad Caverns. A century later, we still haven’t reached the bottom. “Whale of a big cave?” Consider:

Carlsbad Caverns has 120 caves and chambers. With colorful names — Spirit World, King’s Palace, Chocolate High — the caverns dive to 1600 feet. Well over 100 miles of cave passages has been mapped, with who knows how many more miles uncharted. And if caves makes you feel claustrophobic, relax. Because. . .

Entering Carlsbad Caverns, as I did a few years ago, you walk down, down, down through a hole in the ground as tall as a five story building. It feels like hiking into hell.

Once past view of the entrance, you’re on a switchback snaking beneath a ceiling 100-or-so feet above. This is no cave or cavity. This is a world underground.

Stalactites and stalagmites (never mind which is which) lurk at every turn. Other calcite artworks include “popcorn,” “soda straws,” and nature’s own sand castles. You hike down, down, down. Just when you think you can’t get any deeper, the trail bottoms out into the Big Room. Imagine.

Imagine an underground room so huge that it could fit the U.S. Capitol Building inside. The trail around the Big Room loops along for more than a mile. And over the railings the caverns go deeper, deeper. Drop a rock over the edge, as Jim White often did. You hear. . . Nothing.

Once he discovered the caverns, Jim had them to himself for twenty-plus years. Recognizing the wealth of guano they contained, he began bringing the future fertilizer up in buckets. He also used his bucket to lower friends into the abyss. But the caverns and their riches might have stayed a local secret had Jim not let a photographer go down.

In the summer of 1923, photos hit the New York Times. Within months, the new national monument was open for visitors. The following year, with Jim as guide, National Geographic explored the caverns and brought back photos. In 1925, a staircase replaced Jim’s bucket. A year later, the path to the Big Room was built, with lighting installed.

Then in 1930, Carlsbad Caverns National Park began drawing America’s new legions of motor tourists. When the hell-bound entry path proved too daunting for some, an elevator was installed. It still descends — 750 feet — to the edge of the Big Room where, in the 1950s, a restaurant opened.

But unlike many of our overloved national parks, Carlsbad Caverns offers plenty of escape from tourism. And the numbers are manageable, about 400,000 a year compared with 4-10 million in other parks.

Along with roaming far from the maddening crowds, you can take guided tours of Bat Cave, or the more strenuous Slaughter Canyon Cave. Visitors to Spider Cave beware — tight tunnels and crevices await.

While you’re exploring, so are the world’s top spelunkers. These days, some go down, down, then up into overhead caves using ropes floated by balloon over strong stalactites. (Or is it. . .?) New caves were discovered in 2013 and again five years later when two women calling themselves the Twisted Sisters squeezed into The Mystery Room and discovered still more caverns. The Tomb of the Sky Bears, Ladies’ Lament, the Lake of Muddy Misery. . .

There seems no end to Carlsbad Caverns, but once you’re done with life underground, the elevator can take you quickly to the surface. Or hike up, following the light. Jim White would approve.

As he liked to tell and re-tell it, “The beauty, the weirdness, the grandeur and the omniscience absolved my mind of all thoughts of a world above. I forgot time, place and distance. . “

DEEP DOWN IN CARLSBAD CAVERNS