For 400 million years, the Meramec Caverns have been in existence deep in the Ozarks. The caves began forming when water percolating through the bedrock of the Ozark hills began to dissolve the stone, and created the underground passages. Eventually the underground river carved some 18 miles of passageways and chambers, which the seeping water festooned liberally with speleothems – the stalactites and stalagmites that decorate the caverns' floors and ceilings.
The 4.6-mile cavern system holds its place in history as a shelter for pre-Columbian Native Americans, the first cave west of the Mississippi to be explored by Europeans, a saltpeter plant for the Union Army during the Civil War, and a hideout for the notorious outlaw Jesse James.
The caves are now a tourist attraction along former Route 66, and receive around 150,000 visitors every year.