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

A self-built castle made by a mysterious man.

Seemingly grown on some other world, these New Mexico rock formations look like a disused science fiction set.

A hotel and restaurant serving as the mecca of kitsch.

A breathtaking array of ancient Pueblo structures and artifacts counterintuitively preserved by neglect.

This strange seaside tower got its name from a wealthy eccentric who would hide coins among its stones.

An underwater city for the dead.

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

A DIY art gallery/music venue/lecture hall dedicated to video game culture.

Odd outsider art installations surround a Gold Rush-era ghost town.

Possibly the most beautiful carillon in the world, set atop Iron Mountain in Florida.

This abandoned amusement park was built on a site with a dark history.

A hospital closed seemingly in the middle of operations, leaving behind fodder for horror films and ghost hunters.

The first declared National Monument in the United States.

The land is full of geologic eye candy, such as otherworldly spires, mushroom-shaped hoodoos, and prehistoric fossils.

Mysterious rocks that ring musically when struck.

A beautiful 62-acre Catholic shrine and botanical garden.

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

A hand-built folk art installation covered with messages of God's love.

The ghostly remains of an accidental sea.

Hellam Township is reputed to feature seven remote gates, which when passed through in the right order, open an entrance to hell.

Here, at the "world's longest art gallery," you'll find forty miles of ancient petroglyphs and pictographs.

Hidden in the hills of Hollywood, this secluded Oz-themed garden is dotted with dozens of thrones.

A beautiful Victorian-era cemetery, complete with a miniature village.