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

Once the supplier for noteworthy projects like the National Cathedral, this old brickworks now lies abandoned.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A derelict bit of transportation infrastructure hidden in the woods.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

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.

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

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

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

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

The United States Capitol's former columns still stand.

World War II-era bunkers are hidden under the beaches of this picturesque park, which is still scattered with wartime watchtowers.

A wrecked ship dating back to the American Revolution was only recently discovered off the Delaware coast.

Hundreds of antiquated typewriters and office machinery show the technological evolution of business.

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

This collection of odd proofs of concept is like taking a walk through the imagination of a Victorian engineer.

This one-room cabin where the young colonel slept during the French and Indian War.

This rare triple-jurisdiction drawbridge passes through Virginia, Maryland, and Washington, D.C.

This bug-eyed water wheel uses the power of the Sun to clean up Baltimore Harbor.

Once America's tallest structure, now a Baltimore landmark.

A star fort along the C&O Canal in western Maryland that protected America in three wars.

The longest escalator in the Western Hemisphere takes over three minutes to ride down.

This abandoned sea fort has become an accidental bird sanctuary.

The ruins of this long-abandoned unsuccessful gold mine can still be found.