While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

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

Senators used to relax in the nearly forgotten marble tubs now hidden in the U.S. Capitol Building's basement.

Home to a vast and influential collection of Shakespeareana.

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

A fantastic array of trays and cables once whisked books over to the Capitol at 600 feet per minute.

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

The institution is sitting on a goldmine of 21,000 paints, varnishes, pigments, and primers preserved for posterity.

The span is crooked and made from two older recycled bridges.

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 remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

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

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

A rotating cast of guys and dolls in front of a Washington, D.C. building.

A computer bug so primitive it was an actual insect.

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

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

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

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

An obscure public service from the U.S. government that redeems burnt, moldy, and soiled old greenbacks.

It was once the base for a series of domestic terror attacks.

When it opened during the final years of the embargo, all the drinks and cigars were free.

Largest Roman Catholic church in North America.