The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

The highest point in Texas is capped by a big silver pyramid.

A monument celebrating the idea of reaching inaccessible places.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

The deepest lake in the United States, and once the site of epic destruction that lives on in legends.

Only known mainland rookery of the threatened Stellar sea lion.

Home to the deepest rift anywhere on Earth.

The world's first nuclear power plant is open to visitors looking to role-play a meltdown.

Supposedly Satanic numbers adorn this preserved submarine sail.

This highest peak in Idaho can only be reached by traversing a formation known as "Chicken-Out Ridge."

A pop-culture attraction outside of Dyersville, Iowa, hits a home run.

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

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

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

The highest point in Montana is as rugged and singular as the state itself.

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

This picturesque cliffside beacon no longer calls to sailors but shines once a year in honor of a famous shipwreck.

Minnesota's highest point is a scenic vista marked by a plaque and armies of mosquitoes.

The honor of highest point in Michigan was almost given to the wrong peak before this mountain won out by 11 inches.

The highest point in Iowa, while not that impressive to mountain states, has earned its own monuments.

New Brunswick's tallest mountain is the highest point in all the Maritimes.

A toxic ghost town sitting atop a massive coal fire.

Mysterious rocks that ring musically when struck.

The highest point in Delaware is located under a trailer so this marker across the street will have to do.