Depending on who you ask, this controversial treehouse is either a charmingly creative child's playhouse or an illegal encroachment on public land.

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

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

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

For 60 years, the academy had no permanent location until members voted Washington D.C. as its forever home.

A striking memorial to the 21 lives lost in an explosion at the Washington Arsenal

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

They sort through millions of dollars worth of diplomatic gifts on behalf of the government.

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

The grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

A heroic pigeon that, through a barrage of gunfire, delivered a message that saved over 100 lives in World War I.

This taxidermy horse was a Civil War hero.

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

During Prohibition, the U.S. Congress had an "official" bootlegger, with his own Capitol Hill office.

A nostalgic bibliographic gem.

The story behind this beloved toy—named for Theodore Roosevelt and owned by his grandson—is more complicated than you might guess.

A computer bug so primitive it was an actual insect.

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

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

The 28,000-year-old specimen is remarkably intact.

The only Leonardo Da Vinci painting in the Western Hemisphere.

The innocent intentions of this monument are somewhat lost in the sculpture's muscled imagery.

These recently uncovered walls are all that's left of Washington, D.C's first defense contractor.

An ear-piercing buzzer calls lawmakers to a vote with a series of long and short rings to form coded messages.