Mammoth Cave and the Race to Map It

Mammoth Cave in Kentucky is the longest known cave system on Earth, with 685 kilometers of surveyed passages and more discovered every year. Prehistoric Native Americans mined gypsum inside 4,000 years ago, and about 130 species live in its dark, from eyeless fish to cave shrimp. In Mexico, Sistema Sac Actun follows at 386 kilometers of flooded tunnels.

Read how surveyors push the maps deeper and why every rainy season can redraw the rankings of the longest caves on Earth..