Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

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

Washington's iconic carousel has a nice piece of Civil Rights history.

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

Decades before the scandal, this staircase on the river was a literal "water gate."

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

The most accurate timepiece in the world.

Perhaps the most scandalous statue of America's first president.

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

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

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

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

A museum cafe showcases Native American dishes and indigenous ingredients from across the Western Hemisphere.

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

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

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

Home to items never before seen by the public.

The site of the climactic scene from the classic horror film is now a historic landmark.

Royals, rebels, and artists have all conversed at this grand 19th-century Viennese coffee house.

This strange statue features a bust of the famous composer plopped atop a woman's body.

Amidst medieval and baroque buildings, five human-sized gherkins stand tall.

The medieval network of canals hidden underneath the city is opened to explorers each year.

The solemn exterior conceals an opulent interior of this 17th century church.