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

A museum dedicated to the alleged Roswell Incident.

This fast-food outlet is the only space and UFO-themed McDonalds in the world.

The symbol was surreptitiously built into the river bank by German prisoners of war.

The highest paved road in North America winds its way up Mount Blue Sky in Colorado to an altitude of 14,130 feet above sea level.

This hot dog-shaped diner has moved all around Colorado, never been to New York.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

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

There’s a hidden military meme engraved on the World War II Memorial.

An overlooked memorial honoring the local Washington residents who died in World War I.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

The controversial urban planner who designed Washington, D.C., was buried in Maryland, and can presently be found in Virginia.

Soldiers were buried next to Lee's house in the center of Arlington Cemetery to dissuade the general from reclaiming his property after the war.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

The ruins of an important pilgrimage destination for worshippers of a Maya fertility goddess.

The largest retailer of seashells in the world.

Considered by many to be one of the most dangerous highways in Alaska.

This small city where almost everyone lives in the same building can only be reached via North America's longest tunnel.

Running under an entire mountain, the longest highway tunnel in North America is kept fresh using portal fans and jet fans.

A 100-year-old purveyor of curiosities, curios, and kitsch featuring mummies, shrunken heads, and a Fiji Mermaid.

The final resting place of one of the most sensational guitar players of all time was created only after his father got the rights to his music.

This unique library spans a mighty river.

The first declared National Monument in the United States.

The highest point in South Dakota contains the ashes of Valentine McGillycuudy, the "Holy White Man."