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

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

Helen Keller once broke ground on this historic center for the study of technologies to benefit the hearing impaired.

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

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

Home to items never before seen by the public.

Light bulbs, scrap wood, and tinfoil comprise this homemade throne of the gods.

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

The grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

A diminutive memorial marks the site of a successful assassination by a right-wing death squad in America's capital.

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

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

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

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

A line of blue paint marks the route of the inaugural parade.

The bank that helped fund the Mexican-American War and the purchase of Alaska met its downfall after helping Augusto Pinochet launder money.

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

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

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

This grand gothic brewery has been pumping out suds for over a hundred years.

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.