On the Fourth of July this area will transform into a Pompeii-like storm of falling embers and ash.

The first memorial dedicated solely to the Black troops who fought for the Union.

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

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.

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

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

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

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

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

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

The preamble to the U.S. Constitution written entirely from vanity license plates hangs in the Smithsonian museum.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

"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!”

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

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

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

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

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

The oldest continuously operating fish market in the United States.

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

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

Largest Roman Catholic church in North America.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.