This picturesque horseshoe weir was first built in the 1600s to prevent flooding in the town of Bath.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

The 16th-century church was kept in its ruined state as a reminder of the casualties of World War I.

This ancient structure is widely thought to be the oldest intact pyramid in the world.

The ancient abodes are a testament to human ingenuity amid harsh climates.

One of its engravings is believed to be among the first representations of medical and surgical instruments.

The 20-mile causeway that separates the Netherlands from the sea.

A medieval church with largest and oldest collection of Renaissance frescoes in France.

A well-preserved medieval village nested on a rocky outcrop and surrounded by a network of cliffs, natural bridges and canyons.

A series of abstract, silly sculptures represent the works of a great modern classical composer.

The world's tallest bridge is also possibly the most elegant.

This ancient city—home to nine civilizations—is soon to be buried under 200 feet of water.

A centuries-old complex of hand-dug stone chambers has sheltered locals in times of trouble.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the first ‘Harry Potter’ film.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

One of the largest ochre quarries in the world, hidden in a limestone landscape.

This grand hydraulic installation has provided water for townspeople since the Middle Ages.

Founded in 670, this ancient mosque is an architectural time portal.

The other side is actually green.

The oldest known university in the world is in Fez, Morocco.

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

Hundreds of stone stairs and a winding medieval bridge connect this haunting Spanish island to the mainland.

Over the centuries, this island paradise has done it all, from providing monks with ecclesiastical respite to sheltering an exiled Leon Trotsky.

For a brief time in 1960s France, families could climb into a tiny submarine and be pulled along an underwater journey.