After spending the first two days above ground, we ventured beneath the surface at Carlsbad Caverns National Park. It sounds banal, but the only word to adequately describe the caverns is, well, cavernous.

The system of more than 119 limestone caves was designated a World Heritage Site by the United Nations Educational, Scientific and Cultural Organization (UNESCO) because of its cultural, historical and scientific significance, and so it is now legally protected by international treaties.

Both Carlsbad Caverns and Guadalupe Mountains National Parks are part of the Permian-aged (250 to 300 million years ago) Capitan Reef complex, one of the best preserved and most accessible complexes available for scientific study in the world. Researchers can study the reef from the inside through cave passages that penetrate in and through it, as well from the outside through eroded canyon walls.

The cave’s discovery is commonly attributed to James White who, as a 16-year-old cowboy in 1898, ventured toward the cave opening thinking he was seeing smoke from a potentially devastating fire. Instead, he saw bats–thousands upon thousands of Brazilian free-tailed bats flying out of the mouth of the cave. He returned to the cave and began to explore its dark recesses with only a rickety ladder and a crude light source. He would make exploring Carlsbad Caverns his life’s work, spending nearly 50 years promoting the natural wonder to all shared his interest in this underground world.

The gigantic subterranean chambers feature spectacular cave formations and geologic features. It’s difficult to imagine what it must have been like for the first adventurers who walked, then crawled, and finally climbed their way down into the darkness. For our exploration, we opted for the self-guided Big Room Route, a 1.25-mile stroll around the perimeter of the cave’s largest room.

Fair warning: this post is about to go full-on science geek. The cavern’s speleothems, Greek for “cave deposits,” began to develop slowly about a half-million years ago, after the cavern had formed. At that time, the climate was wetter and cooler, allowing water to drip down into the limestone bedrock and into the cave. As the water trickled downward, it absorbed carbon dioxide gas from the air and soil, which formed a weak acid. As this acidic water dissolved a little limestone it absorbed the basic ingredients needed to build most cave formations — the mineral calcite. Once a drop of calcite-laded water emerged in the cave, carbon dioxide escaped into the cave air, making the water incapable of holding its tiny mineral load. Gravity pulled the water droplet downward, leaving the calcite behind. Slowly, over time, these mineral deposits became the geologic formations we see today: stalactites and stalagmites. Other processes led to different types of formations, but the essential ingredient — water — continues to shape the speleothems today.

Exploration of Carlsbad Caverns continues. In 1986, cavers discovered an even larger cave system adjacent to Carlsbad Caverns that extends over 140 miles. Deep with Lechuguilla Cave, scientists have discovered enzyme-producing microbes capable of destroying cancer cells, as well as other clues to life on — and under — the earth.

Three things we learned today worth sharing:

1. Despite all appeals to reason and all outright prohibitions, cave visitors will not only touch cave formations but also step off the trails to snap selfies without regard to potential damage and permanent staining.
2. Many people, if given the opportunity, will cut in line.
3. An overweight, middle-age guy with one leg who uses crutches sets the bar pretty high. If he can make it around the trail, anyone can.