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

Home to items never before seen by the public.

The oldest continuously operating fish market in the United States.

The national park was once a plantation estate.

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

Please don’t anchor your boat onto the Department of Defense’s underwater data cables.

This lovely picnic spot featuring thunderous jet landings is an aircraft spotter’s dream.

The graveyard holding the remains of George Washington's slaves was forgotten for nearly 200 years.

The romance of early commercial flight still fills this Art Deco destination.

The 72-foot giant escaped confinement in a large patch of mulch only to be reburied in the sandy shores of the Potomac River.

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

A mammoth pair of Civil War artillery guns abandoned out in the forest.

A former major munitions plant that has been converted into a sprawling art space.

A superbly preserved example of Georgian residential architecture that was once home to one of the founders of Alexandria, Virginia.

An original apothecary from 1792.

America's first federal monument.

This colonial tavern played host to George Washington, Thomas Jefferson, and other famous early Americans.

The narrowest house in America is seven feet of pure spite.

The final resting place of an unidentified revolutionary soldier sits behind a Virginia church.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

A hot dog stand where the heads are just as hot as the dogs.

This whimsical Oz-themed park had a wonderful impact on the surrounding neighborhood.

No one knows how many bodies are in this vault in a Chicago public park.

Once the product of an inexplicable gold strike, this ghost town is now home to one man and his love of classic machines.