A turn-of-the-century architectural marvel built on healing mineral springs and salt licks.

The world's longest known cave system.

The largest earthwork effigy in the world.

Ohio's 19th-century communist micro-society.

Funded by John D. Rockefeller, this is one of the earliest, and most beautiful, shopping arcades in America.

Ghost stories surrounded this “castle,” the only structure from a huge mansion that was never built.

The only presidential monument to display a late POTUS's actual casket.

Known as "The Dome" this is the world's largest open air geodesic dome.

The world's tallest doric column is this Ohio monument to a naval victory in the War of 1812.

The twin towers in this Chicago fountain use 50 foot tall video screens to spit on people.

What's left of the ruins of the 1893 Columbian Exhibition, or World's Fair, also known as the White City.

This historic hotel invented the chocolate brownie.

A century-old hotspot for jazz, frequented by everyone from Charlie Chaplin to Al Capone.

An antiquated German apothecary on Chicago's North Side.

A lush green oasis in the middle of Chicago.

A Victorian cemetery in the heart of Brooklyn remains a popular mecca of morbid curiosity.

Sniff the Titan Arum's rotting flesh.

Ride the subways of yesteryear.

Dedicated to one of the darkest moments in Irish history, this memorial has faced its fair share of backlash.

A former waterfront market is now in the center of town due to some interesting Boston engineering.

The site of Paul Revere's historic two lantern warning.

Two thousand artifacts from around the world collected by one woman who loved to travel.

An enormous, inside-out glass globe built in 1935.

This solitary convex mirror sculpture at an abandoned ferry station at the edge of a fjord reflects the scenery back at the viewer.