These abandoned waterworks are crumbling into the Potomac River.

A surprising, but overlooked example of geology in the middle of the nation’s capital.

They sort through millions of dollars worth of diplomatic gifts on behalf of the government.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

There just so happens to be a court even higher than the U.S Supreme Court: a basketball court in the building itself.

100 years later, they're still down there.

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.

Amid the sprawling Defense Intelligence Agency Headquarters is one of Washington's least accessible museums.

There’s a special club house at the top for the bell ringers.

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

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

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

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

The "lovely red Vega" of the legendary record-settling pilot.

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

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

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

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

Four bald cypress trees in Lafayette Square, across from the White House, mark the southern edge of a 100,000 year old cypress swamp.

The most accurate timepiece in the world.

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

A computer bug so primitive it was an actual insect.

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