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

Corn-inthian columns with a uniquely American take on neoclassical architecture.

The elevator that makes it possible to fly American flags in bulk over the U.S. Capitol

This unique historical monument features large concrete spheres designed to resemble fallen stars.

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

A traveling postal dog covered 48 states and more than 140,000 miles, and he lives on as taxidermy, patched up with a rabbit's foot and a pig's ear.

Decades before the scandal, this staircase on the river was a literal "water gate."

Need a hardcopy of the 50-title Code of Federal Regulations? This is the place.

The U.S. Fish Commission’s effort to mass produce carp.

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

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

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

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

A much-maligned monument to teetotalism.

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

Perhaps the most scandalous statue of America's first president.

A clone of a cloned tree that was so important it allegedly had its own guards.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

A wondrous old library overlooking the nation's capital.

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

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

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