More than 12,000 years ago, this park was a playground for mastodons.

The longest of the four remaining covered bridges in Missouri.

An underground river pushes more than 200 million gallons out of this Missouri spring every day.

Some of the oldest exposed rock formations in the United States.

A historic, scenic mill that was forced to close due to overlogging.

Around 50 million gallons of water flow from this spring every day.

A 40-foot waterfall flows into this unique natural swimming hole.

An average of 33 million gallons of water pour out of the collapsed cave at the heart of this spherical spring.

These pink granite water slides are the result of millions of years of erosion.

Often referred to as the largest spring in America.

One of the deepest springs in Missouri.

Stand at the point where the two mightiest rivers in the United States converge.

A mythical bird etched into the face of a rock doubles as the mascot for a nearby school.

A celebration of the animation wizard's childhood home and antique railroad memorabilia collection.

This former small town was destroyed not by the motor oil it sprayed the ground with but by the toxic waste that was added.

A museum and gift shop in a small Illinois town commemorates the work of E.C. Segar and the local figures on whom he based his characters.

What was once a presidential estate is now an exotic menagerie and home to the Budweiser Clydesdales.

A geological oddity formed by two rivers carving out a mass of limestone on both sides.

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

The history of the treatment of mental illness, illustrated in all its gory detail, and housed in an asylum.

Once an ambitious nature spa, these forest ruins now provide a serene monument to failure.

There just so happens to be a court even higher than the U.S Supreme Court: a basketball court in the building itself.

The walls of the iconic dome are hollow and have a secret stairway.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.