The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

This limestone outcropping was once a ceremonial site for ancient Native Americans.

This abandoned asylum was once a state of the art facility before devolving into one of the most deadly mental institutions in American history.

The site of the one of the most deadly train wrecks in American history.

Don't get it twisted: This is the oldest pretzel bakery in the United States.

The rustic think-space of famed naturalist John Burroughs stands exactly as he left it.

Come for the chanting, stay for the monastical vegan buffet.

An eccentric priest's tribute to George Washington, this chapel tells the story of the American Revolution.

This mansion turned restaurant was once a pitstop for Al Capone during his travels.

A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

It marks the spooky spot where the bodies of two young boys were found in the 19th century.

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

The first and only carousel with a lineup entirely of insects.

A historic landmark and museum filled with curious objects representing the history of Key West.

The oldest farmer's market in America is so ancient it was approved by the King of England.

Electrical pylon in the shape of Disney's beloved mouse.

This kitschy tavern is also home to rare early editions of "Treasure Island."

A monument marks the location of the first successful steamboat demonstration.

This statue inspired by Renoir's famous painting embodies the jovial spirit of Key West.

An eccentric aristocrat brought these Australian natives to their current Scottish home.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

This replica of the Greek structure is in the heart of Nashville.

This historic train station has been converted to a locomotive themed hotel.

All you ever needed or wanted to know about America's favorite whiskey, but not a drop to drink.