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

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

When it comes to handsignals (and colonialism) rock always beats scissors.

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

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

Obscure Freemasons still live in D.C.’s largest private residence.

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

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

Before Nixon, "watergate" meant canals.

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

A celebrity from the late Cretaceous period.

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

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

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

A nostalgic bibliographic gem.

The walls of the iconic dome are hollow and have a secret stairway.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

A derelict bit of transportation infrastructure hidden in the woods.

The house where John Wilkes Booth conspired with his co-conspirators.

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

Largest Roman Catholic church in North America.

"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 oldest continuously operating fish market in the United States.