Mammoth Cave, the world's longest known cave system, stretches 426 miles under Kentucky. The cave's limestone began forming 330 million years ago when the region was submerged under an ocean. Visitors ...

The Sistema Huautla in Oaxaca is the 10th deepest cave on Earth, and a explorers with a 2023 expedition to map the system have added over 700 feet to its length. When you purchase through links on our ...

Deep below Earth's surface, rock and mineral formations lay hidden with a secret brilliance. Under a black light, the chemicals fossilized within shine in brilliant hues of pink, blue and green.

Sometimes, a hole in the ground is just a hole. Other times, it’s a portal to an underground cave spanning miles in width and length. You don’t really know what’s inside unless you dive into the void.