400 million-year old limestone caverns nestled in the Ozarks served as shelter and a hideout for cultures throughout North American history.

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

Historic funicular railway, believed to be the shortest railroad in the world.

One of the most scenic stretches of road in America winds between some of the country's oldest trees.

This monument to a veteran of the Mexican-American War is one of only two in Manhattan that serve as an actual mausoleum.

A commemorative plaque hides a door that leads down to the New York Public Library's underground book bunker.

Built hundreds of years ago this downtown iron barrier once protected a much despised king.

A dark patch of the ceiling at Grand Central Terminal which was not restored is still stained brown by tobacco.

Avoid gangster interaction while window-shopping.

This sculpture by artist Fritz Keonig survived the 9/11 attacks and now stands as a monument to the victims.

A popular European tradition makes its way to the states on one of America's most famous bridges.

Try not to get slimed in Tribeca.

The fanciest public restroom in New York City boasts fresh flowers, art, and a classical music soundtrack.

The warmest cave in the Ozarks features two seemingly bottomless lakes.

This historic hotel on Bathhouse Row in Hot Springs National Park has a storied history of gangsters and baseball greats.

An extravagant western hotel where every floor is the "ground floor."

This monumental Jesus is often referred to as "Our Milk Carton With Arms."

A hillbilly theme park that proved so unpopular the land wouldn't even sell on eBay after it closed.

This century-old roadside attraction is full of bizarre rock formations.

This haunted hotel built on natural springs once served as a hospital for a quack doctor promising a cure for cancer.

The only diamond mine in the world where you can keep what you find.

The enormous 250-room Vanderbilt mansion conceals hidden doors and secret passageways.

Elvis's own personal tropical hideaway.

This Memphis recording studio launched the careers of Jerry Lee Lewis, Johnny Cash, and Elvis Presley.