A secret greenspace hides atop a Capitol parking garage.

Every drop of D.C. tap water flows through this old waterworks.

An obscure federal monument honors the French diplomat who served as Ambassador to the U.S. during WWI.

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

The U.S. Navy’s preposterously detailed mini battleship took 77,000 hours to complete.

This taxidermy horse was a Civil War hero.

This grisly headstone doesn’t seem to be resting in peace.

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

‘Bush the old fire dog died of poison July 5th, 1869. RIP.’

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

An 18-mile-long tunnel for sewage waste will soon wind within the bowels of Washington, D.C.

Part of a WWII submarine is lurking outside the Washington Navy Yard parking lot.

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

Where you can hail your favorite fictional commanders-in-chief.

Through the decades, Black music stars have performed at this historic hub for music and the arts.

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

The 28,000-year-old specimen is remarkably intact.

During Prohibition, the U.S. Congress had an "official" bootlegger, with his own Capitol Hill office.

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

More than 500 unique and specially designed cases collected by D.C.'s "Harmonica Case Man."

The school tested mustard gas for the U.S. Army during World War I.

A small token of gratitude from freezing cold journalists who were given a warm haven while covering JFK's inauguration.

Atop this media building, two hives containing more than 30,000 bees keep the surrounding area vibrant.

This nine-story building is the oldest standing skyscraper in D.C.