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

A huge musical instrument played by the ocean.

This Native American settlement dates back to the Pueblo II period.

The remnants of a creative early method of wildfire prevention.

The world's only teal arches exist in a city that cares more about its aesthetic than an Instagram influencer.

The world's largest military aircraft cemetery.

A spiritual vortex among the red rocks in Sedona.

The solitary grave of a schooner captain killed by lightning while serving biscuits.

This estate on the banks of the James River was home to a Founding Father, two presidents, a famous bugle melody, and what some say was the actual first Thanksgiving.

A former major munitions plant that has been converted into a sprawling art space.

A genuine Tudor manor transported piece by piece from England.

An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

An unusual geological feature towers over the remains of a dark episode in United States history.

At the time of its completion, it was the tallest dam in the world.

Around half a million years ago, these magnificent columnar basalt cliffs were formed from cooling lava.

A former pillar of the Black community in Ellicott City.

Although built to generate electricity for Marylanders, this dam has become an all-you-can-eat buffet for American bald eagles.

FDR's Art Deco hospital tower was hopelessly inefficient.

Once a thriving business district, this former shopping area is now an urban ghost town in the heart of the city.

This abandoned sea fort has become an accidental bird sanctuary.

Considered by many to be one of the most dangerous highways in Alaska.

Running under an entire mountain, the longest highway tunnel in North America is kept fresh using portal fans and jet fans.

The ruins of a town wiped out by the second-largest earthquake in recorded history.

This small city where almost everyone lives in the same building can only be reached via North America's longest tunnel.