Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

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

A clear blue swimming hole with hidden caves, still unexplored.

Hollywood's most famous landmark, the "temporary" sign that has stood for decades longer than intended.

Rock face that shares a name with Mary Shelley's famous doctor.

This immigrant bridge once spanned the Thames but is now a fixture of an Arizona city.

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

The ghostly remains of an accidental sea.

This Pringle-shaped ledge makes for the perfect photo op.

Behind this beachfront shop lies a spectacular, colorful sea cave with an equally colorful past.

This futuristic bridge is one of the longest self-anchored pedestrian bridges in the world.

This Detroit ruin was once a gothic bastion of its community, but now it stands as a haunting ruin.

The bones of an old zoo crumbling in the shadow of a new one.

This old cement mine has been used as everything from a mushroom farm to a recording studio.

An unfortunate geological resemblance to Satan has labeled this Pasadena gorge as a passage to the underworld.

America's most famous piece of self-built architecture.

Hidden in a secluded Greek cove is a pristine beach marred only by the rusting smuggler's hulk stranded on its shores.

A theme park that suffered massive flooding during Katrina was abandoned, and now proves irresistible to trespassing explorers.

Decades after testing the polio vaccine on unwitting patients, this historic mental hospital sits in ruin.

A Canadian POW for German soldiers during WWII where prisoners hatched an elaborate escape plan.

Once the longest bridge in Ireland, this rusting span sits abandoned and overrun by nature.

One of the world's largest automobile junkyards is a unique landscape of metal and moss.

A Hawaiian stairway to heaven—that you can't climb.