Carlsbad Caverns National Park

Listen for a moment. Up here, the Chihuahuan Desert is dry and bright. Wind moves through creosote bushes and spiky lechuguilla plants, and the sun bounces off pale limestone. Then the trail turns, and the ground drops away into a vast, dark mouth in the hillside. The air coming out of it feels cool and damp on your face. It smells of wet stone and earth, and faintly of the animals that live inside. This is the Natural Entrance to Carlsbad Caverns. It sits in the Guadalupe Mountains of southeastern New Mexico, in Eddy County.

Before we go down, it helps to know what kind of rock surrounds you. These mountains were once an ocean reef. Hundreds of millions of years ago, during a period geologists call the Permian, a warm inland sea covered this region. Sponges, algae and other small marine life built up a huge reef along its edge. Geologists call it the Capitan Reef. Over time the sea dried up, and the reef was buried under salt and sediment. Much later, the land lifted and eroded, and the old reef came back to the surface as the ridges you see today.

Here is the first surprise. Most caves in the world are carved slowly by water that is only slightly acidic. Carlsbad is different. Geologists believe this cave was dissolved from below by sulfuric acid. Gases rich in hydrogen sulfide rose from oil and gas deposits deep underground. When those gases met oxygen-rich groundwater, they formed sulfuric acid. That acid ate through the limestone and opened enormous rooms. One clue remains inside — thick, chalky deposits of gypsum, a mineral left behind by that chemical reaction.

People knew about this opening long before anyone mapped it. Native American groups lived in this region for thousands of years, and pictographs and cooking sites have been found near the entrance. In the late nineteenth century, local settlers noticed something strange on summer evenings. A dark column rose from the hillside, twisting into the sky like smoke. It was not smoke. It was bats — hundreds of thousands of them, leaving the cave to hunt insects over the desert.

The man most often linked to the cave's exploration is Jim White, a young cowboy from the area. According to his own account, he saw that column of bats around the end of the nineteenth century and went to find its source. He made a ladder from wire and sticks and climbed down with a kerosene lantern. Over the following years he explored deeper and deeper. He later guided early visitors, lowering some of them into the darkness in a bucket once used for mining.

That bucket points to a less romantic chapter. In the early twentieth century, the cave was valued mainly for bat guano, the droppings piled on its floors. Guano is a strong fertilizer, and miners hauled tons of it out to sell to farmers, some as far away as California. The work was hard and the smell was intense. But it brought people and attention to the cave. Photographs of the rooms below began to circulate, and the wider country started to take notice.

The government moved to protect the site in the 1920s, when it became a national monument. In 1930 it became a national park. Much later, in 1995, UNESCO added it to the World Heritage List. That is the global list of places considered important to all of humanity. The recognition covers more than this one cave. The park protects well over a hundred known caves, hidden inside the same ancient reef.

One of those caves is a second surprise. In 1986, cavers dug through rubble in a pit here and broke into a passage called Lechuguilla Cave. It turned out to be one of the deepest and longest caves in the United States. It holds rare crystal formations and microbes that scientists study for clues about life in extreme places. Lechuguilla is closed to the public to protect it. You will not see it today, but it lies beneath the same desert you are crossing.

Now, the walk down. The Natural Entrance trail switchbacks steeply into the darkness. It descends roughly the height of a seventy-story building, so take it slowly and watch your footing on the damp pavement. As daylight fades behind you, your eyes adjust. Look for formations with names given by early guides — Devil's Spring, the Whale's Mouth, Iceberg Rock. Notice how quiet it becomes. The only sounds are footsteps, low voices, and the slow drip of water somewhere in the dark.

The air down here stays cool all year, at roughly thirteen degrees Celsius, whether it is midsummer or midwinter above. Every drop of water that falls carries a tiny load of dissolved minerals. When the water evaporates or loses carbon dioxide, it leaves that mineral behind. Over enormous spans of time, those deposits grow into stalactites hanging from the ceiling and stalagmites rising from the floor. Some are thin hollow tubes called soda straws. Others are knobbly clusters called cave popcorn.

Then the passage opens into the Big Room. It is the largest single cave chamber by volume in North America. A loop trail of more than a kilometre circles its floor, and the ceiling disappears into shadow far above. Along the way, look for the Giant Dome, a massive column of stone, and the delicate Doll's Theater. Near one edge, the Bottomless Pit drops into blackness. It does have a bottom, of course — but early explorers dropped stones into it and could not hear them land.

A few practical notes. Formations grow incredibly slowly, and the oils on human skin can stop that growth, so keep your hands to yourself. Stay on the paved path. Wear shoes with good grip and bring a light layer for the cool air. Elevators connect the visitor centre to the cave level, so you can walk down and ride back up. In the warm months, rangers often lead an evening program to watch the bats emerge. The bats usually leave for Mexico as autumn ends.

Before you leave the Big Room, stop and switch off any screen for a moment. Let your eyes rest on the nearest column of stone. Every ridge on its surface came from one drop of water after another, over an almost unimaginable stretch of time. Above you, the desert is hot and bright, and the ancient reef holds this silence in place. When you ride back up into the daylight, notice the smell of dust and sun again — and how loud the world suddenly feels.