The privately owned cemetery that holds room for Washington's finest when they step down from life.

This leafy estate is worth $18 million and is so grand it has two mailing addresses.

A painfully obvious spy house sits right across the street from the Russian Embassy.

An Industrial Revolution-era public work that purified water using nothing but sand.

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

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

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

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

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

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

Seemingly unremarkable items like empty sushi trays, chef hats, and freshness stickers are being preserved so future generations can look back on this beloved cultural import.

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

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

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

After his presidency, George Washington planned to live only a few blocks from the Capitol building.

A computer bug so primitive it was an actual insect.

The tunnel under the Capitol Building where Congress takes out its trash.

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

This nine-story building is the oldest standing skyscraper in D.C.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

Giant acorn-shaped 19th century gazebo from which suburban Washingtonians gazed upon the original "silver" spring.

Literal "money laundering."

Where the U.S. government kept its actual treasure, before Fort Knox.

The first presidential bomb shelter was located in an old vault under the Treasury, connected to the White House via tunnel.