The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

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

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

Look closely and you’ll notice that the color changes a third of the way up the tower.

An overlooked memorial honoring the local Washington residents who died in World War I.

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

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

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

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

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

A traveling postal dog covered 48 states and more than 140,000 miles, and he lives on as taxidermy, patched up with a rabbit's foot and a pig's ear.

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

Perhaps the most scandalous statue of America's first president.

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

The national park was once a plantation estate.

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

Largest Roman Catholic church in North America.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

A derelict bit of transportation infrastructure hidden in the woods.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

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

The United States Capitol's former columns still stand.