The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

A giant "X" symbolizes the blood spilled from the brutal Juárez drug wars.

During the summer, surfers in Alaska take advantage of this inlet’s unusual water patterns.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

A line of blue paint marks the route of the inaugural parade.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

The school tested mustard gas for the U.S. Army during World War I.

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

A historic arena where the Beatles played their first concert in the U.S.

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.

A brass plaque dedicated to a convicted cannibal hangs in the National Press Club, and that's not even the craziest part of the story.

The most accurate timepiece in the world.

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

The oldest continuously operating fish market in the United States.

The national park was once a plantation estate.

Largest Roman Catholic church in North America.

The most decorated dog of World War I is preserved in the Smithsonian.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

The massive, original Colgate Clock is mounted on a defunct factory building that was once a prison.

This modern castle sat empty for decades before a fire inspired its builders to complete its luxury halls.

This chapel on a cliff is renowned for its healing powers and was founded on the site of a supposed divine intervention.

The once highest point in China blends symbolic design with a kick of adrenaline.

The remains of this visionary community can still be found much as it was a century ago.

Home of an evil witch famous within southern folklore.