Washington's top-secret Cold War-era doomsday communications tower is located in a small neighborhood park.

Art deco landmark on the outskirts of Washington, D.C.

A building shaped like the Army Corps of Engineers logo, because why not?

This unacceptably tall building was the real reason for Washington, D.C.'s skyscraper ban.

A historic ruin just 20 feet away from a busy highway onramp.

The only Civil War battle in Washington D.C. took place near this highest natural point in the city.

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

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

There's a crumbling old mansion inside the Smithsonian National Zoo.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

A nostalgic bibliographic gem.

An Industrial Revolution-era public work that purified water using nothing but sand.

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

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

A derelict bit of transportation infrastructure hidden in the woods.