This 14th century castle withstood years of battle but is now sliding off the hills into the Danube.

The first island in the world designated a light-pollution-free astronomical observation point.

The very center of Paris is surrounded by a bevy of strange good luck rituals.

An exquisite tunnel of cascading flowers.

Recently restored menagerie of Victorian-era beasts.

Visitors to this library are in for a real-world education in modernist architecture.

A brooding mansion of clinker brick stands out among the Victorian houses of Pacific Heights.

A natural arch offers panoramic views of Yangshuo's karst hills.

This massive library holds what was once the largest book collection in the world.

Along a California highway is a kind of Jurassic Park made of metal.

St Bernard de Clairvaux Episcopal Church, better known as one of the oldest European buildings in the Western Hemisphere.

A centuries old castle atop a dormant volcano houses museums devoted to both women and witches.

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

Rippling sand dunes frozen in the Arizona rock.

Dramatic river bend surrounds a natural red-rocked pedestal.

Most-visited and most-photographed slot canyon in the American Southwest.

A minotaur, a labyrinth, and a dubious restoration pull in visitors from around the world.

A city built from mud and known as the "Manhattan of the desert."

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

142 ceramic steps become a mosaic once a year.

This huge metal monument is slowly being stripped to its concrete skeleton.

A museum marks and documents the site of the Titanic's launch.

Ruins of a Carnegie family mansion on Cumberland Island.

Nondescript elevator doors open to reveal a stunning, surreal world.