The first declared National Monument in the United States.

This shallow pit was once used to send over 20,000 buffalo plummeting to their death.

The highest point in South Dakota contains the ashes of Valentine McGillycuudy, the "Holy White Man."

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

A six-ton, 12-foot-tall concrete prairie dog is touted as the largest in the world.

This simple badlands butte is the highest point in North Dakota and may be the only high point to charge admission.

Inside this museum resides a boot fit for a giant.

Giant six-pack could provide one person a six-pack a day for 3,351 years.

What was once the second largest steel mill in the US is now a sprawling complex of modern ruins.

This castle was once considered as an option for the Royal Family's alternate residence, but you may know it better from the 'X-Men' movie.

An operating lighthouse from the 1860s.

This landmark is a central figure in the Nez Perce origin story.

Derelict buildings are all that remain of a complex at the site of one of the worst mining disasters in Montana history.

An entire city block built completely out of petrified wood.

The world's largest Holstein cow.

A true roadside icon standing on the same plains that the herds once roamed.

Hidden in magnificent rolling countryside, see what may be the largest modern stone circle in the world at Wisconsin's very own "Stonehenge”

This long unused shot tower on the Mississippi remains a point of pride for a small city in Iowa.

For just a few bucks, this Iowa funicular will let you feel like an 1800s fat cat.

A sprawling outdoor museum filled with larger-than-life works of art.

The evolution of recreational vehicles and motorhomes is on display in the “RV capital of the world."

Ghost stories surrounded this “castle,” the only structure from a huge mansion that was never built.

This former hub for crafty philosophers was founded by a writer who died aboard the infamous RMS Lusitania.

A reproduction of a giant humanoid "fossil," a hoax buried locally for construction crews to find and gain national attention.