The stunning cave in Naica, Mexico, is home to some of the largest crystals on Earth, but harsh conditions can kill those who stay too long.

Two 325-million-year-old ctenacanth shark fossils discovered in Mammoth Cave shed light on ancient marine ecosystems.

At 4.3 miles long, Parks Ranch Cave in southeastern New Mexico is the second longest gypsum ... dangles from a cottonwood branch over the warm, crystal-clear Black River. Veni steps into the ...

Natural Trap Cave is a pit in northern Wyoming into which countless animals have fallen and met their untimely demise since the Pleistocene. Paleontologists today find the cave a treasure trove — a ...

High in the mountains of Guerrero, Mexico, a spelunker and her guide entered a narrow limestone cave they believed had ...