An 800-year-old island castle in Guernsey's main harbor.

Underground hospital complex constructed by slave laborers during the German occupation of the Channel Islands.

Still standing despite its considerable slant, this tilted lighthouse has become a local symbol of resilience.

An island graveyard with spectacular views of the Caribbean.

The ruins of an important pilgrimage destination for worshippers of a Maya fertility goddess.

A Lovecraftian altar of nightmarish bronze chairs sits ominously on a boardwalk in Puerto Vallarta.

Clap your hands at the base of the pyramid, and the song of a sacred Mayan bird will echo through the air.

Underwater art project will double as a massive artificial coral reef to help regenerate the damaged ecosystem.

Morocco’s modern capital was once a haven for Barbary pirates, who went so far as to establish a republic of their own.

God's Saharan sandbox of wrath.

The courtyard of this small Marinid madrasa is a dazzling example of intricate Islamic architecture.

The oldest monument in Marrakesh and the city's only surviving example of Almoravid architecture.

Vast stretch of tide-pools with a unique Moroccan charm.

Thousands of narrow alleyways in an ancient medieval city make up what's believed to be the world's largest car-free urban zone.

An awe-inspiring mosque in Morocco with one of the tallest minarets in the world.

Traditional 11th-century outdoor tannery.

The other side is actually green.

It took 40 years to build this Eden-like garden in Marrakech, later restored by Yves Saint-Laurent.

Founded as a refugee camp, now a popular tourist spot.

Morocco's Argania trees are infested with nut-hungry goats.

The platform atop this verdant volcano was built with the help of a royal elephant.

New Zealand's epic shrine to all things puzzling.

A galaxy of glowworms—larvae of a gnat—hides deep in the belly of these caves.

This electric green sulphur lake in New Zealand looks like a cartoonish radioactive dump site.