One of the few surviving "Wigwam"-themed motels.

The world's longest known cave system.

The farm where one of America's greatest leaders was raised is now a well-appointed landmark.

The longest navigable underground river in the United States is home to countless blind and albino animals.

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

This former tuberculosis research hospital endeavored to cure the dreaded disease with fresh air and positive attitudes.

Ruined pieces of stone and a swimming pool are all that remain of an amusement park swept away by a flood.