An obscure federal monument honors the French diplomat who served as Ambassador to the U.S. during WWI.

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

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

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

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

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

The only National Monument ever to go missing for nearly 50 years then resurface in a dump.

A historic arena where the Beatles played their first concert in the U.S.

One of the largest artillery pieces in the world sits in a Washington D.C. parking lot.

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

The span is crooked and made from two older recycled bridges.

You could be standing at the site of one of D.C.'s most fatal tragedies and not even know it.

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

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

The oldest continuously operating fish market in the United States.

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

A museum cafe showcases Native American dishes and indigenous ingredients from across the Western Hemisphere.

A painfully obvious spy house sits right across the street from the Russian Embassy.

The United States Capitol's former columns still stand.

The site of the climactic scene from the classic horror film is now a historic landmark.

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

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

A Norwegian-born sculptor created these soaring guardian angels at the entrance to Hoover Dam.

The most magnificent bottle house in a town strangely full of them.