This quarter-mile tunnel under the Bluff in Pittsburgh bends at a 45-degree angle.

Dyed by iron oxide over centuries, these sandstone rocks rise thousands of feet into the sky.

A drab two-story office space in Delaware is a hidden tax haven for Hillary Clinton, Donald Trump, and over half the Fortune 500 companies.

This weeping, 10-foot-tall sculpture was a maquette for a 9/11 memorial.

This local gem houses the largest collection of pre-Raphaelite paintings outside of the U.K.

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

A blend of art, antiquities, and Americana fill this museum, surrounded by whimsical, enchanting gardens.

What began as an art installation is now the private drinkhaüs for a brewery's employees.

Francis Julius LeMoyne built this crematory in 1876; he was the third person to be cremated here.

This spot memorializes one of the greatest plays in NFL history, unless you happen to be a Raiders fan.

"Where the ducks walk on fish."

The Cold War-era "underground Pentagon" is a sprawling subterranean hideaway for the Defense Department.

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

Where the oil industry began.

What looks like a simple quaint estate in rural Pennsylvania was in the 18th century home to a small monastic community.

The sounds of the world's largest fully functioning pipe organ dazzle shoppers at a Philadelphia Macy's.

This dramatic rail curve was once the target of a failed Nazi attack.

Behold the rickety wooden glory of the world's oldest operating roller coaster.

These disused steel furnaces are now haunting ruins that may one day be a national park.

This elaborate towering structure was once famed for its revolutionary height.

The pop art icon's gravesite is broadcast 24 hours a day on his museum's website.

This titanic java kettle is one of the many kitschy landmarks located along America's OTHER famous highway.

Yo, Adrian!

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.