A geological bull's-eye visible from outer space.

Climb atop one of the world's longest and heaviest trains for an unbelievable journey across the Sahara Desert.

This remarkably well-preserved mosque stands amid an 11th-century caravansary.

Five ancient libraries, little changed for centuries, preserve a medieval archive of Quranic lore and civic documents

Yugoslavia's biggest underground airport lies in ruins.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

The remains of a sunken military ship wreck visible through clear water.

This unique structure allowed boats to bypass underwater mine barriers in the channel to enter the harbor.

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

Just a few miles from Novalja, a strange geological oddity has left scientists baffled.

This heart-shaped island looks substantially less lovely after a recent bulldozing project.

Now harmless, this looming post struck fear into the heart of medieval troublemakers.

A musical instrument played by the sea.