One of Scotland's most important modern structures, it just made the '100 Most Endangered Sites' list.

A Museum of Psychiatry in a still-operating mental institution.

The enigmatic and seldom visited ruins of a Mayan city-state.

Every equinox this Maya pyramid puts on a spooky ancient light show.

The only electricity pylon under whose legs you can go by boat.

It houses the remains of a 17th-century version of the Titanic.

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

A wall of chewing gum moonlights as collective art.

An explosion of natural color known as "the river that ran away from paradise."

Venice's island of the dead.

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

A historic house left in "dramatic still life."

The lake that fills and empties itself at random.

The seawater playground of gilded-era San Francisco burned to the ground in 1966.

Monasteries on rock pillars, once accessible only by frayed ropes.

A haunted hill that supposedly defied gravity.

A miniature world of concrete and stone in Springfield, Ohio.

Museum dedicated to awful artwork.

A large camera obscura, constructed entirely from digitally fabricated components.

The struggle of a small Dutch island against the sea.

The only structure left with direct ties to the Salem witchcraft trials of 1692.

An accidental trick of light casts the perfect shadow of a pilgrim of the Camino de Santiago against the cathedral wall.

An collection of Chinese propaganda posters from 1949 to 1979.

A Mysterious Masonic tomb in San Luis Obispo.