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

A much-maligned monument to teetotalism.

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

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

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

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

Art deco landmark on the outskirts of Washington, D.C.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

Once the supplier for noteworthy projects like the National Cathedral, this old brickworks now lies abandoned.

The most accurate timepiece in the world.

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

A historic ruin just 20 feet away from a busy highway onramp.

An obscure public service from the U.S. government that redeems burnt, moldy, and soiled old greenbacks.

The only Civil War battle in Washington D.C. took place near this highest natural point in the city.

Housing the National Women's Party since 1929, this historic house is now a monument to the fight for gender equality.

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

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.

Home to items never before seen by the public.

Memorial to the 137 lives lost on a ship fire, the whole hulk of which washed up on the Asbury Park shore.

On the Hudson resides one of the largest clocks in the world.

Infamous marsh filled with toxic waste, World War II-era London rubble, and dead mobsters galore.

A giant light 13 feet high shines near Thomas Edison's old Menlo Park lab.

These unassuming lighthouses have seen the first reading of the Pledge of Allegiance, the first wireless transmission, and more than one mystery.