At 207 feet, one of the world's longest continuous escalators.

This house was once the location of Frelinghuysen University.

Dedicated to the man who created the first radio wave communication system.

An 18th-century townhouse that once hosted guests of the president.

A brass and marble scale model of the solar system embedded in the concrete.

Coins and medals straight from the mint await visitors to this shop in the nation's capital.

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

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

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.

The tunnel under the Capitol Building where Congress takes out its trash.

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

An ear-piercing buzzer calls lawmakers to a vote with a series of long and short rings to form coded messages.

A secret greenspace hides atop a Capitol parking garage.

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

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

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

A portal into the bricked up canal that runs through the heart of Washington D.C.

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

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

A hidden passageway now marks the site of an assassination attempt on Ronald Reagan that some say broke a 140-year-old curse.

These abandoned waterworks are crumbling into the Potomac River.

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

Before Metro, Washington had a robust streetcar network—and you see the remains of this infrastructure if you know where to look.

Behind an abandoned storefront is an example of pioneering 1930s gas station architecture.