The Veryovkina Cave was the deepest-known cave on Earth, and experts stumbled upon it before daring to attempt a dangerous mapping of the depth.

From the deep ocean floor to vast underground caverns beneath our feet, these places challenge our understanding of the world.

The Hranicka Abyss is at least 1,325 feet deep, and likely goes down further. — -- A team of explorers believe they have discovered the deepest known underwater cavern the world in eastern Czech ...

BOB MARSHALL WILDERNESS, Mont. — Montana calls itself home to the first and now second deepest cave in the continental United States. A team discovered Bobsled Cave in the Bob Marshall Wilderness, and ...

This summer, Richard Brown and five others from around the country hiked almost 30 miles into the Bob Marshall Wilderness to explore an underground wilderness few have seen. More people have walked on ...