Even in this modern era of hyper-connectivity and interplanetary exploration, Earth still offers a few corners — and holes — left to discover. Author James Tabor documents one such pilgrimage in his enthralling book “Blind Descent: The Quest to Discover the Deepest Place on Earth.”

He wastes no time in describing the dangers of extreme caving, with the book opening on the words, “Stop. We have a fatality,” scrawled on a jarringly white piece of paper strung across a cave passage more than half of a mile below the surface at Cheve Cave in Mexico.

Supercaves, as they are known, have long remained one of the last frontiers for exploration upon this planet. Since the realm of caving is literally underground, it is often forgotten, and it is rarely documented with photographs. Accessing their deepest points is not for the faint of heart; tight squeezes, deadly stagnant air, flash floods, toxic sulfuric acid drips and poisonous spiders are par for the course, but explorers must also get past the first danger of navigating near-vertical tunnels in absolute darkness for often weeks on end.

“Blind Descent” details the parallel attempts by lifelong professional cavers Bill Stone, an American, and Ukranian Alexander Klimchouk. Each man was driven by a similar quest, but his motivations were quite different. For Stone, science was the focus, a way to answer questions about the planet we inhabit. “The search for the deepest cave on earth is the greatest epic of discovery and adventure you’ve never heard of.” For Klimchouk, the science took backseat to the thrill of adventure.

Stone’s particular obsession was Cheve Cave in Oaxaca, Mexico, and everything else in his life subsequently took a backseat to the many expeditions that consumed his time. His marriage, his family and his financial security all fell away as he drove himself and his teams deeper and deeper, past physical and psychological barriers that would have stopped less determined individuals.

Two Different Kinds of Men

Tabor paints a captivating picture of this complicated man, a tall and imposing figure with an intense presence. Stone refused to be ignored; he had a reputation for being a tough leader, too willing, many said, to put people in risky situations to reach his goal. Tabor describes him as a “classic alpha male and a Type-A personality.”

In contrast, Klimchouk is characterized as small in stature, quiet and patient. Unlike Stone, he believed “that supercaves required multigenerational efforts.” He was a firm believer in delegating roles and leadership to others. Where caving broke apart Stone’s family, it became a shared endeavor for Klimchouk’s, and Tabor shows him as a committed family man, introducing his children to the caving experience at a young age.

Tabor lines up the stories of these two men against each other, laying out the steps each took to lead their teams to be the first to reach the bottom of the world. With each successive expedition, Stone was convinced Cheve would push deeper still, all the way to the world record, and he returned year after year in an attempt to prove it, though at the time there were eight caves in the world known to be deeper.

Klimchouk had similar plans, with his aim focused in the Arabika Massif region in the Republic of Georgia. Throughout decades of exploration, pushing the Krubera Cave became the Ukranian caver’s dream. Unlike Cheve cave, which is in the tropics and descends from a massive maw in a cliff side, Krubera begins as little more than an inconspicuous sliver in the tundra, high above timberline in an alpine setting. Near vertical in many places, including one tunnel that falls for 500 feet, Krubera has the added challenge of being cold, and constant water and wind make navigating it a struggle to keep hypothermia at bay, all conditions that make it more debilitating more quickly.

Tabor compares the art of deep cave exploration to climbing Mount Everest, but in reverse, with the most exhausting parts coming on the second half — the ascent back to the surface. Stone calls it akin “to ascending El Capitan, through a waterfall, at night.”

Setting up camps underground means cavers spend extended hours with no daylight, which can greatly impact a body, as sleep-wake cycles go awry. Hallucinations are not unusual, and bodies become more susceptible to injuries and illnesses.

For readers, most of whom will never set foot in a supercave, Tabor brings the experience close, deftly evoking that tormenting darkness, as well as the exhaustion, the terror and the thrills, which very often seem to be the same thing. “Blind Descent” is a heart-pounding and riveting plunge into the depths of the Earth.