For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

The large rock formation where the Shawnee prophet Tenskwatawa stood and encouraged his warriors during the Battle of Tippecanoe.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

Beautiful waterfalls grace a canyon visibly torn by a violent tornado.

These sub-farmland caves are home to a majestic stalactite known as the "Crystal King."

Take a drunken tour inside the world's largest known geode.

This Detroit ruin was once a gothic bastion of its community, but now it stands as a haunting ruin.

Abandoned concert venue legendary for its rock counterculture.

The only freestanding table rock formation east of the Mississippi.

The longest navigable underground river in the United States is home to countless blind and albino animals.

An ancient chamber filled with wonderful rock art and a Neolithic carving of a human face.

A hidden oasis just two minutes from downtown Atlanta.

The lighthouse central to the 1980s horror classic "The Fog" is, in fact, located in one of the foggiest areas of the Pacific Coast.

These hellish-looking cliffs in the Canadian Arctic have been burning for centuries.

This lonely tomb is all that remains of a once-bustling ancient trade hub visited by Marco Polo.

A staggering number of rock carvings in an abandoned quarry.

The library houses an incredible collection of some of the world's most impressive books and manuscripts.

This spectacular mosque houses the second-largest chandelier in the world.

The decaying remains of a once-luxurious Soviet spa town.

This unique 230-foot waterfall is a natural beauty hidden within the vast wild landscape.

An impressive armored bronze effigy marks the tomb of one of the medieval era's greatest warriors.

Terraced flowerbeds and rock sculptures in the midst of the Minnesota wilderness.

The oldest colonial fortress in the Americas was once the home and later prison of Christopher Columbus.

A spectacular hidden beach in Ireland has the dark, disturbing nickname of "Murder Hole Beach."