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

A promising candidate for the lost rock laid by George Washington was unearthed, but the hunt is still on.

This groundbreaking 16th-century map is known as "America's birth certificate."

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

Once a sewer culvert, this road tunnel now offers cyclists and pedestrians a subterranean stroll under the C&O Canal.

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

The walls of the iconic dome are hollow and have a secret stairway.

This statue of the "father of television" stands prominently in the United States Capitol.

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

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

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

This historic boathouse was constructed using salvaged lumber from burned barns.

The National Park Service’s best-kept secret with views that rival any in D.C.

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

A muscular Art Deco monument represents the struggle between regulators and unbridled markets.

A spectacular tribute to statesman and philanthropist Andrew Mellon.

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

A building shaped like the Army Corps of Engineers logo, because why not?

Garments from across the globe call this hidden gem home.

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

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

The hippo that stands on this university campus was once a drunken flea market purchase.

Disks are rolled out onto the south lawn to absorb the impact of Marine One's wheels like giant coffee coasters.

Beneath unsuspecting visitors feet, a capsule containing pieces of America’s civil rights history.