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

Obscure Freemasons still live in D.C.’s largest private residence.

An overlooked oasis of quiet on the grounds of Washington's monumental basilica.

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

A celebrity from the late Cretaceous period.

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

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

A super-sized promotional trick that is now a D.C. landmark.

The oldest continuously operating fish market in the United States.

The national park was once a plantation estate.

There's a crumbling old mansion inside the Smithsonian National Zoo.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

A Spiritualist house of worship where believers communicate with the dead in the spirit world.

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

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

A wondrous old library overlooking the nation's capital.

A historic neighborhood church is reborn as a psychedelic arts collective.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

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

The home of the first American-born saint is one of the only curved buildings in New York.

An uber-secure, windowless tower of doom in the center of Manhattan is an NSA spyscraper.

A restaurant on Staten Island showcases a different grandmother’s cooking every night.

Dodge prohibitionists and slide through the telephone booth in Crif Dogs.

A room in New York City that contains 250 cubic yards of dirt worth a million dollars.