These huge gypsum crystals in Mexico's Naica caves, some up to 12m long, have been growing for tens of thousands of years -- but scientists have only now discovered what's inside them. "We've ...

Some of the Earth's most incredible features lie beneath its surface. Caves often hold fascinating secrets, from the world's largest underwater cave, which is full of human remains, to the Cave of the ...

More than 900 feet beneath a mountain in northern Mexico, there’s a hidden chamber that almost doesn’t look real. Massive, glass-like crystals stretch in every direction, some as long as a city bus.