An Industrial Revolution-era public work that purified water using nothing but sand.

A nostalgic bibliographic gem.

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

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

Housing the National Women's Party since 1929, this historic house is now a monument to the fight for gender equality.

There just so happens to be a court even higher than the U.S Supreme Court: a basketball court in the building itself.

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.

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

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

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

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

This lovely picnic spot featuring thunderous jet landings is an aircraft spotter’s dream.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

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

The "lovely red Vega" of the legendary record-settling pilot.

The oldest continuously operating fish market in the United States.

A much-maligned monument to teetotalism.

Before founding the American Red Cross, Clara Barton had a tremendous humanitarian impact by locating thousands of missing soldiers.

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

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

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

Look closely and you’ll notice that the color changes a third of the way up the tower.

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

Right next to departures—how convenient!