Parts of this former military training ground may have inspired parts of J.R.R. Tolkien's famous fantasy series.

This was the first homestead registered after President Abraham Lincoln signed the Homestead Act into law.

When an ancient supervolcano erupted, some of Nebraska's prehistoric animals were forever preserved in ash.

Underneath downtown Lincoln resides a network of caves that was also the city's first brewery.

This little gem of a museum is a hidden jewel filled with prehistoric treasures.

This replica small town lets visitors take a stroll through the story of progress in the U.S. via thousands of Americana artifacts.

This improbable contraption was passed down through five generations of industrious Tennesseans.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

Aqueducts have dramatically changed this old lake, now home to tufa towers and its very own species of tiny brine shrimp.

A massive volcanic plug is now a protected area that hosts a number of bird species.

One of the world’s largest and deepest freshwater springs, where mastodons once roamed.

At this Minnesota state park you can easily wade across the source of the mighty Mississippi.

The only Florida state park with publicly accessible caves.

Stroll through a wonderland of stupendous moss-covered trees.

The fifth-longest natural arch in the world, and the longest outside China.

The marker offers a rare chance to be in four U.S. states at once, though there's some controversy over its geographic accuracy.

This spectacular track has run continuously since 1882.

John Hendrix predicted the creation of the "Secret City" built as part of the Manhattan Project.

This former maximum-security prison is creepy, sobering, and supposedly haunted.

A bronze sculpture honors the 12 black students who attended the first integrated public high school in the segregated South.

Better known as the "Body Farm," this unique research facility has been studying how human bodies break down since the 1980s.

In one of America’s oldest mountain ranges, a long-awaited section of a scenic highway is now open to the public.

Mile-long cave system near Great Smoky Mountains.

This museum pays tribute to the Cherokee leader who created a written language for his people.