One of the largest artillery pieces in the world sits in a Washington D.C. parking lot.

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

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

Largest Roman Catholic church in North America.

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

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

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

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

Fittingly, America's museum of architecture is itself a magnificently designed old building.

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

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

The United States Capitol's former columns still stand.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

Extraordinary objects lurk in this quintessential regional museum.

This pun was simply waiting to come to life, and one defense contractor made it so.

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

This museum explores the grim reality of life in the earliest British colonies in America.

The rogue roots are gradually consuming some of the historic marble grave markers.

An original apothecary from 1792.

Edgar Allan Poe's old dorm is now a shrine to the author's legacy.

An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

A secretive collection featuring objects that were designed specifically for U.S. intelligence operations.