The only arched bridge made of stone on the entire Mississippi River.

17,400 lbs., 12 feet in diameter, and 29 years in the making.

This large midwestern cavern features impressive rock formations and an underground waterfall.

Equal parts record-breaking temple to consumerism and bizarre fun park, it's more than you think it is...

The famed architect designed this Minnesota gas station of the future with a lookout tower.

This sky-high radio mast is formerly the tallest man-made structure in the world.

The U.S.' first commercial park dedicated entirely to flying drones.

One North Dakota man's vast collection of rare rocks, polished orbs, and geological wonders.

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

On the windswept Dakota plains there is a memorial to circus workers who were struck down by lightning.

A monument to the center of the North American continent may be off by a few miles.

These former Cold War launch sites have been preserved for tourists to see where the button might have been pushed.

The remnants of an early American attempt at missile defense.

One devoted couple has donated multiple recreations of Michelangelo's sculptures to this South Dakota town.

Thanks to a loophole in property ownership, this alleyway has become a cacophonous street gallery.

Hidden behind Lincoln's head is a 70-foot-long chamber containing enamel plates documenting American history, sealed in a teakwood box in a titanium vault.

These early tent-shaped grave coverings are unique to Appalachia.

A key producer of charcoal iron in the early 1800s, the structure still stands today.

Once decrepit and slated for demolition, now one of the longest pedestrian bridges in the world.

Over a dozen Native American earth mounds dating back over 2,000 years dot this Tennessee archaeological park.

All you ever needed or wanted to know about America's favorite whiskey, but not a drop to drink.

This Memphis recording studio launched the careers of Jerry Lee Lewis, Johnny Cash, and Elvis Presley.

More than five miles of underground passageways.

The secret city built by the Manhattan Project.