These azure waters were thought to lead to the Mayan Underworld.

A magical sinkhole on the Yucatán Peninsula is adorned with mini waterfalls and hanging vines.

Few of the many visitors to this resort town know of its hidden Maya ruins.

"Dark Sky Park" is heaven on Earth for astronomers, one of the rare U.S. locations with no artificial light pollution.

This Pennsylvania cave holds evidence of the oldest known inhabitants of North America.

This lush forest valley was once mined for lumber to the extent that it was once nicknamed "The Pennsylvania Desert."

A record-size collection of wild-haired troll dolls tells the story of the mythical creature's roots in Scandinavian folklore.

A winding, cliffside stretch of road overlooking the Delaware River.

This park contains a number of standing stones meant to heal and inspire.

Once the world's largest reinforced concrete structure, this abandoned bridge now beckons urban explorers.

A historic grist mill and active sluice on the Black River.

The headquarters of the Fraternitas Rosae Crucis, complete with Rosicrucian pyramids, all in the Pennsylvania woods.

A miraculous natural phenomenon known as "the spring that breathes."

Native Americans built this circle of stones, which was used to predict astronomical events.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

A beautiful geyser under environmental threat.