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

The institution is sitting on a goldmine of 21,000 paints, varnishes, pigments, and primers preserved for posterity.

The span is crooked and made from two older recycled bridges.

Washington's top-secret Cold War-era doomsday communications tower is located in a small neighborhood park.

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

The national park was once a plantation estate.

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

A fantastic array of trays and cables once whisked books over to the Capitol at 600 feet per minute.

100 years later, they're still down there.

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

The towering figures were created from the cemetery's fallen old-growth trees.

Before Nixon, "watergate" meant canals.

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

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

Go take a picture with the inventor of the daguerreotype photographic process.

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

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

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.

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

It was once the base for a series of domestic terror attacks.

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

There’s a hidden military meme engraved on the World War II Memorial.

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