Berthed at the Charlestown Navy Yard in Boston, "Old Ironsides" is the oldest commissioned warship still afloat.

Standing in a state of "arrested decay," this ghost town allows for a detailed peek into Gold Rush life in an unusually harsh climate.

This volcano rises like a giant anthill from the plains below, with a road spiraling up to the rim.

A small metropolis of Pueblo cave dwellings have been carved right into the hillside of this national monument.

The tragedy of the Japanese internment camps is remembered here by a stark "Soul Consoling Tower."

The second-largest ceremonial mound in the United States is an artificial hill that is loosely shaped like a pentagon.

The museum chronicling a treasure hunter's dream, fulfilled.

The famous boat that once ferried Bogart and Hepburn still floats in Key Largo after being abandoned for years.

A historic presidential getaway on the continental United States' southernmost island.

This iron and wood Civil War city-ship was the first vessel to be sunk by an electrically detonated torpedo.

One of the only Florida forts to remain in the hands of the Union all through the Civil War still stands as a historic stronghold.

The tech giant built three enormous glass orbs in Seattle so employees could work inside a rainforest greenhouse.

A wall of chewing gum moonlights as collective art.

Two cannon-like cranes were installed on top of the bank building to fend off bad feng shui.

Home to items never before seen by the public.

A stunning Catholic cathedral built by a curve-loving communist in Brazil’s newly created capital.

Lone survivor from Custer's Last Stand forever preserved.

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

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

A pair of giant legs paying homage to a poem, a king, and it would seem, socks.

Tribute to the famous Notre Dame football coach who died in a plane crash.

It's big, it's a ball, and it's made of twine—the world's largest of its kind.

Famous church recognized for both its unique design and disciplined monks that live according to the Benedictine discipline.

This art deco masterpiece was once a miracle spring mecca but is now simply a government office building.