The world's largest boar is a huge steel titan found at a French rest stop.

The site of the first medieval crusade that pitted Christians against Christians.

This army of concretions is an unexplained geological phenomenon unlike anything else in the world.

The castle was reconstructed to fit Kaiser Wilhelm II's romanticized vision of the Middle Ages.

Despite centuries of architectural innovation, this French castle is being built like it's the 13th century.

A mud statue stands in the dark tunnels, seeming to hold up the weight of the city above.

The tradition of open-air secondhand and antiquarian bookselling in Paris dates back to the Renaissance.

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

This French castle is said to have once held the Holy Grail but is now a gorgeous mountaintop ruin.

This structure atop a craggy cliff in one of the most beautiful parks in Paris boasts an unbeatable view.

The world's largest reflecting pool is just two centimeters deep.

The narrowest street in Paris.

Remains of Roman amphitheater hidden in a sleepy quarter of Paris.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

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

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

This massive library holds what was once the largest book collection in the world.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Bali's remote "gateway to heaven" is one of the most sacred places on the island.

Hindu temple of the dead home to hundreds of long-tailed macaques.

A secluded, little-known temple hidden amid the dense jungle.

A small 12th-century temple surrounded by waters believed to have curative properties.

This impressive clifftop temple was once at the center of an international custody dispute.