Hidden beneath a bridge, this waterfall is known for the large amounts of graffiti painted on its base.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

A well-preserved Ancestral Puebloan ruin tucked beneath a desert cliff.

Quite simply the largest tree in the world (by volume).

An optical illusion found amid a logged redwood forest.

This massive redwood tree has a hole in the base big enough to drive through.

One of the most scenic stretches of road in America winds between some of the country's oldest trees.

Canyon walls shrouded in ferns.

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

A one-of-a-kind sundial at the Very Large Array honors a radio astronomy pioneer, incorporating the original piers from his breakthrough radio telescope.

The massive, incredibly rare instrument is over 11 feet tall with a range so deep it goes lower than humans can hear.

Make a wish at what might be America's only Catholic shrine to a sinner.

America's only nuclear missile silo open to the public.

The fading, forgotten remains of a once bright and booming factory.

This immigrant bridge once spanned the Thames but is now a fixture of an Arizona city.

In Tucson a giant metal snake helps pedestrians cross a busy highway.

The world's largest military aircraft cemetery.

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

A disquieting Aztec sculpture displays hundreds of stone skulls representing the victims of human sacrifice.

This ceremonial Mexican square looks as though it belongs in a science fiction movie.

A graceful natural rock formation stands astride the point where the Gulf of California meets the Pacific Ocean.

An indigenous take on European design creates a stunning visual overload.

Clap your hands at the base of the pyramid, and the song of a sacred Mayan bird will echo through the air.

This fantastical house shaped like a seashell brings aquatic design to architecture.