Imagine the surprise of young lumberjack, Ho Khanh, a native of Vietnam's then-sleepy Phong Nha township, when he saw enormous, ethereal columns of fog billowing out of the ground, like the earth ...

Highlights of the five-night trip include seeing the cave’s own rainforest and a calcite wall called the Great Wall of Vietnam. Vietnam is home to the world's largest cave. It's so vast that it has ...

Divers in Mexico's Yucatan Peninsula say they have discovered the world's largest underwater cave. Underwater archaeologists discovered last week that the cave system known as Sac Actun, located near ...