For many years, the origin of these enigmatic artificial caves was the subject of debate among historians.

Continental Europe's only museum devoted to salt and pepper shakers features more than 20,000 designs.

This 47-story "M" needed 20 years to be completed

You'll need a microscope to see some of the minuscule masterpieces in this modest museum.

Legends surround this natural rock formation that looks like a Moorish king wearing a crown.

Down this yellow brick road, visitors are treated to toadstool houses and massive mushroom sculptures.

The world's most elegant power lines.

On a trail in Portugal's Barão de São João National Forest, a pile of faces look up at hikers from the forest floor.

Bacteria and algae give the salty water its bubblegum hue.

An ancient Roman theatre restored to its former glory in the Spanish city of Cartegena.

A micro-communist utopia in Spain with no police, no mortgages and full employment.

A Spanish town built into the cliffs.

The world's largest wooden structure.

An eerie collection of the surviving structures from a past celebration of the future.

The Roman city was the birthplace of various emperors and is home to one of the empire's most impressive architectural feats.

An enchanting landscape of ancient sandstone structures eroded into otherworldly shapes.

Peek into a cave of giant, glimmering crystals.

The extensive relics of an ancient Roman and Phoenician fish processing plant hide in a town park.

Spanning the El Chorro gorge, this pathway used to be one of the most dangerous crossings in the world.

This quaint Spanish village agreed to be painted blue as a marketing stunt but found that they preferred it that way.

The ruins of a 2,000-year-old Roman fishing village perched on one of the best beaches in Spain.

An otherworldly art experience.

This centuries-old tower hosts endangered bald ibis mating pairs and looms over a pristine beach.

Considered the birthplace of the Copper Age and Bronze Age, the river is tinted red from 5,000 years of mining.