An old hill fort covered in over 100,000 crosses is a symbol of Lithuanian nationalism and beliefs.

An underwater city for the dead.

An experimental, automotive replica of Stonehenge.

The explorer Captain Cook may have named it White Island, but the Maori call it Te Puia o Whakaari – The Dramatic Volcano.

Ghosts of France's colonial past.

The anatomical-pathological collection of a man who changed surgery.

Space-age monument to an early 20th-century uprising.

Paris' fabled purveyor of exotic taxidermy and natural history curios.

A marvel of Byzantine engineering under the streets of Istanbul.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

Mutant vegetables, transgenic mosquitos, and atomic rodents span the walls of this one-of-a-kind museum.

The origin of this mechanical boy was a mystery until he revealed his maker by writing it in perfect cursive.

This golden temple is surrounded by hundreds of stone tablets that comprise the "world's largest book."

Surreal riveted sea forts once protected the Kent shores from German attack.

A spherical "micro-nation" in the heart of Vienna.

A castle hand-built by a Spanish dreamer in the Australian tropical jungle.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

This odd Chilean waterfall-cano hotel must be entered via a rope bridge.

A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

Iceland's "Smoky Valley" is a beautiful river that is shrouded in a constant cover of steam clouds.

This beautiful natural train tunnel is said to grant the wishes of visiting lovebirds.

Hot springs monkey spa in the middle of Hell's Valley.

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

Part modern art project, part traditional chapel, this see-through church is only substantial from the right angle.