A mysterious monument meant to be a guide into "an Age of Reason" was destroyed after an apparent bombing.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

A modernist landscape of water and sci-fi concrete.

An arsenic-filled pool in the Grand Canyon takes on the appearance of a giant, overflowing pumpkin.

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

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

A breathtaking array of ancient Pueblo structures and artifacts counterintuitively preserved by neglect.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

The largest earthwork effigy in the world.

The only swimming pool listed on the National Register of Historic Places is emptied and refilled each day with naturally filtered water.

A picture-perfect town, perfect for blowing up.

The world's longest known cave system.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

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

Paranormal experiences in this hotel's room 217 led Stephen King to write "The Shining."

Possibly the most beautiful carillon in the world, set atop Iron Mountain in Florida.

Manhattan’s Battery Park has a whimsical carousel full of spinning, glowing fish.

A rare view of a preserved Victorian science museum.

A natural gas leak provides a flickering flame beneath a waterfall.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

Panorama exhibition hall in old silent theater with a beautiful backyard garden.

A beautiful geyser under environmental threat.