The largest self-built castle in the U.S., six decades in the making.

A hidden network of subterranean passageways lies tangled beneath Indianapolis' bustling City Market.

This grand gothic brewery has been pumping out suds for over a hundred years.

Breathtakingly blue walls shimmer inside the "Glacier Behind the Town."

It's not hard to see why the historic Peabody Conservatory of Music's library has been described as a "cathedral of books."

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

The hike through a narrow river flanked by the 2,000-foot-tall walls of Zion Canyon is one of the best in the world.

The world's longest known cave system.

The magic's in the hole!

In the middle of an extremely unforgiving and desolate high desert is the most secret military facility in the world.

This symbolic piece of New Orleans architecture is also home to a few ghastly stories.

Two thousand artifacts from around the world collected by one woman who loved to travel.

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

An underwater city for the dead.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

An abandoned facility that has become a place of ritualistic satanic worship, or so rumor has it.

Where America's first doomsday cult awaited the end of the world.

A museum and shop on Bourbon Street located in the former home of the second Voodoo Queen of New Orleans.

The oldest cemetery in New Orleans, resting peacefully for over 200 years now.

Home to items never before seen by the public.

The first declared National Monument in the United States.

Home of an evil witch famous within southern folklore.

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

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.