D.C. once had its own tiny rival to the New York Stock Exchange.

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

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

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

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

Corn-inthian columns with a uniquely American take on neoclassical architecture.

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

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

The district's only illusionarium supports free writing programs for local students with every purchase.

These abandoned waterworks are crumbling into the Potomac River.

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

This restaurant has been a haven for D.C.'s LGBTQ community since the 1950s.

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

"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!”

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

This unique museum cafeteria showcases the history and regional diversity of African American cuisine.

Sit where JFK proposed to Jackie or where Nixon dined on meatloaf at this storied pub.

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

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

They sort through millions of dollars worth of diplomatic gifts on behalf of the government.

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

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

Before founding the American Red Cross, Clara Barton had a tremendous humanitarian impact by locating thousands of missing soldiers.

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.