The former home of Samuel Clemens and family remembers the happiest period of the author's life.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

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

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

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

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

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

The "lovely red Vega" of the legendary record-settling pilot.

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

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.

The controversial urban planner who designed Washington, D.C., was buried in Maryland, and can presently be found in Virginia.

A muscular Art Deco monument represents the struggle between regulators and unbridled markets.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

Largest Roman Catholic church in North America.

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

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

Home to items never before seen by the public.

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

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

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

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

The grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

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

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