The world's longest known cave system.

This high point in the Great Smoky Mountains is said to be home to the chief of all bears.

An abandoned town is hidden in Great Smoky Mountains National Park.

The highest point in North Carolina and the United States east of the Mississippi River, Mount Mitchell is named after argumentative explorer Elisha Mitchell.

Despite violent work crews and massive delays this abandoned canal tunnel was built to last into the modern day.

Spectacular mineral formations fill these caves, which have been used for everything from smoking meat to stashing illicit liquor.

This university transit system is a 1970's vision of the future.

A miniature golf course crafted inside the world's largest simulated cave.

The penultimate and final resting places of British General Edward Braddock—minus a few bits and pieces.

The Paul Bunyan of the steel industry.

This advertisement for talcum powder was painted on the rock face and has since defied removal.

A cave on the Maryland border where civilians took refuge during the bloodiest battle of the Civil War.

A star fort along the C&O Canal in western Maryland that protected America in three wars.

The fifth-longest suspension bridge the world, connecting one Michigan peninsula to another.

This shallow cave got its name from copious amount of human bones found inside.

Island where motor vehicles are banned -- home to the only carless highway in the United States.

A harrowing trail up a mile-high mountain.

An enormous effigy of the goddess of compassion hides within the sanctuary.

The Chinese have long been excellent at the art of copying, but this epic replica takes the biscuit.

The earliest pagoda built in the beautiful Panmen Scenic Area of Suzhou.

Thanks to a bit of wordplay, seven auspicious stone cats guard this ancient canalside street.

A large visitor's complex and place of remembrance on the outskirts of the DMZ.

South Korea's largely symbolic, barely used gateway to the North.

The best place for scenic views of the DMZ and North Korea.