This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

The installation’s official name, “You Who Are Getting Obliterated in the Dancing Swarm of Fireflies,” says it all.

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

Dramatic river bend surrounds a natural red-rocked pedestal.

Most-visited and most-photographed slot canyon in the American Southwest.

Rippling sand dunes frozen in the Arizona rock.

This memorial pyramid marker honors one of the United States Government's first official camel riders.

The shop's owner has spent decades in the desert wearing nothing but a strategically placed sock.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

At this research institute, the chile is king.

This is one really big nut.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

People escaping slavery may have hidden inside a corpse vault.

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

A nostalgic bibliographic gem.

The walls of the iconic dome are hollow and have a secret stairway.

A historic estate packed with George Washington's heirlooms, and its own nuclear bunker.

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

A painfully obvious spy house sits right across the street from the Russian Embassy.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.