This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

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

This might just be the TARDIS of bookstores.

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

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

An FDR-era tuberculosis sanatorium has stood abandoned in the suburbs of the U.S. capital for over 30 years.

The American Revolution was galvanized into serious action due to the tragic clash with British soldiers that occurred at this location.

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

This simple stone memorial remembers a secret, Geneva Convention-defying interrogation base from WWII.

Parking garage where Bob Woodward met Watergate source "Deep Throat."

The bank that helped fund the Mexican-American War and the purchase of Alaska met its downfall after helping Augusto Pinochet launder money.

This Niagara Falls tourist trap is a world bright with neon and curiosities that will inspire love, hate, or a mixture of both.

A historic Montreal market that was the city's agricultural hub for over century.

The North Carolina grounds are leased in perpetuity to the British Commonwealth for as long as the WWII sailors are buried there.

An intricately designed junk art house with four extravagant junk art cars hidden in the suburbs.

Decades before the scandal, this staircase on the river was a literal "water gate."

Giant origami sculptures tucked into desert scenery beckon passers-by to explore further.

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

A restored Pittsburgh house of God has been converted to a marvelous house of suds.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

This public park was the site of the largest civilian disaster of the Civil War.

A museum commemorating the Donora Smog, which killed 20 people in October 1948 and sparked national outrage over air pollution.

Once the most painted on object in the world, this short campus fence is well on its way to being so again.

A portion of the old Pirates stadium over which a defining home run once flew still stands even after the rest of the stadium was torn down.