Weeki Wachee Springs State Park in Florida has enchanted visitors since 1947 with underwater performances by "real" mermaids.

It may sound like something out of a nightmare, but scientists say they weren’t dreaming when they discovered a massive ...

The Hranicka Abyss is at least 1,325 feet deep, and likely goes down further. — -- A team of explorers believe they have discovered the deepest known underwater cavern the world in eastern Czech ...

I'm a severe claustrophobe. After getting trapped in a slide in my local McDonald's at five years old, I swore off all tight and dark spaces forever. So it's not entirely surprising that I couldn't ...

June 15, 2006 — -- "Nightline" joined forces with writer Tim Zimmerman and filmmaker Gordon Hiles, who documented an ambitious dive to one of the world's deepest, most dangerous underwater caves.

Hells Canyon, the deepest river gorge in the United States, likely got rapidly carved 2.1 million years ago when a shifting landscape in Idaho caused a giant lake to start overflowing. That's ...

On this episode, we hear how a team of researchers at the University of Northern Iowa is exploring the deepest caves in the U.S. with NASA funding. This could inform the search for life on other ...