An architect's childhood fantasy treehouse made real.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

The first declared National Monument in the United States.

The only royal palace on U.S. soil has been a territorial capitol, a military headquarters, and a prison for a queen.

An authentic replica of an Asian temple and garden hidden amongst the natural beauty of Hawai'i.

Watch the newest land on the planet form before your eyes.

This black shoreline is made up of exploded lava particles.

This historic hotel on Bathhouse Row in Hot Springs National Park has a storied history of gangsters and baseball greats.

Some North Carolina Cherokee have been keeping their history alive for decades with a single play.

This high point in the Great Smoky Mountains is said to be home to the chief of all bears.

The uniquely-designed winter home and sculpture studio of Anna and Archer Huntington.

The museum chronicling a treasure hunter's dream, fulfilled.

A historic presidential getaway on the continental United States' southernmost island.

"We Seceded Where Others Failed."

A monument celebrating the idea of reaching inaccessible places.

The former home of the Nobel Prize-winning American writer is now home to dozens of six-toed cats.

The romance of early commercial flight still fills this Art Deco destination.

At 207 feet, one of the world's longest continuous escalators.

A Memphis park where you can walk the whole Mississippi River in one go.

The secret city built by the Manhattan Project.

After a water tower painting was accused of being an ad, a simple fix was made that gave the city a motto.

The world's longest known cave system.

The fifth-longest suspension bridge the world, connecting one Michigan peninsula to another.

Island where motor vehicles are banned -- home to the only carless highway in the United States.