The iconic D.C. restaurant where the Cuban Missile Crisis was negotiated, now a Walgreens.

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

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

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

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

Politicians, bureaucrats, and military officers gathered in this field near the Capitol to settle their disputes with blood.

Former villa and estate of James Deering developed to preserve native tropical forests.

With nickel-steel armor and three-inch thick bullet resistant windows, FDR's train was a rolling fortress.

Remains of a historic fountain that was mysteriously lost in the demolition of a D.C. traffic circle.

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

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

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

Helen Keller once broke ground on this historic center for the study of technologies to benefit the hearing impaired.

The sci-fi villain is a little-known inhabitant of the U.S. capital's largest cathedral.

The most accurate timepiece in the world.

This evocative New Jersey statue memoralizes the Polish victims of a Soviet massacre.

Hidden in plain sight on the Hudson River is an abandoned train station where nature has taken over.

This historic iron-working village is now a ghost town so immaculate that it looks as though it was recently built.

A failed piece of Orientalism has become the proud symbol of a community.

A scenic fort on the harbor protected Philadelphia from an attack that never came.

The internal railway of one of the biggest steel plants in America has been transformed into a linear park with unique industrial views.

One of the world's largest model railroads is a mind-boggling achievement.

This Delaware River bridge is emblazoned with a catty slogan from a more prosperous time.

This palatial botanical garden is home to one of the largest pipe organs ever installed in a private residence, and a piece of Wood's cycad.