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

A much-maligned monument to teetotalism.

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

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

This poor little statue is the most vandalized memorial in Washington.

Art deco landmark on the outskirts of Washington, D.C.

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

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

A celebrity from the late Cretaceous period.

A small triangle of DC grass is the final resting place of one of Sonny and Cher's songs.

A hoard of sky catalogs, astrophysical journals, even the works of Galileo and Copernicus.

A historic ruin just 20 feet away from a busy highway onramp.

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

An unassuming, powerful monument north of the U.S. Capitol bears witness to the resilience of Japanese Americans during a time of grave injustice.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

The national park was once a plantation estate.

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

Once the supplier for noteworthy projects like the National Cathedral, this old brickworks now lies abandoned.

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

You could be standing at the site of one of D.C.'s most fatal tragedies and not even know it.

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

The only Civil War battle in Washington D.C. took place near this highest natural point in the city.

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

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