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

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

An 18-mile-long tunnel for sewage waste will soon wind within the bowels of Washington, D.C.

These abandoned waterworks are crumbling into the Potomac River.

Part of a WWII submarine is lurking outside the Washington Navy Yard parking lot.

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

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

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

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

A diminutive plaque recalls the treetop sniper who almost killed Abe Lincoln.

This robust fence in front of a historic Georgetown home is likely made from hundreds of recycled Revolutionary War firearms.

The discovery site of the "Capitalsaurus," the official dinosaur of Washington, D.C.

There's an old indoor swimming pool hidden directly underneath the White House Press Briefing Room.

This forgotten boat elevator was an engineering marvel in its heyday.

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

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

"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 hidden offices underneath Memorial Bridge have been locked up since 1976.

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

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

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

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

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

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