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.

Historic medieval fortified city in southwest France.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

A fortified palace in the shape of a ship on the Thiou river.

An opulent monument built for a duke who donated his entire fortune to the city of Geneva.

A 2017 crowdfunding campaign saved this historic castle from being destroyed.

France's high-tech, future-themed amusement park.

This ancient theater was once the home of fierce gladiatorial battles.

Thousands of flamingos and other bird species flourish in these Camargue wetlands.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

This home designed for chocolate magnate Antoni Amatller is an exquisite treasure-box of Catalan Modernism.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

A Gothic cathedral created from volcanic rocks.

Hundreds of hidden passageways weave through the old quarters of Lyon.

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

An 18th century fountain and two columns are all that remains of Rome's forgotten river harbor.

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

Breathtaking and huge 430 year old maps of Italy.

The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

A forgotten "city of water" underneath the famous Trevi district.

A monumental fountain in Rome features a large statue of Moses that has been criticized for centuries.

Installed in an act of one-upsmanship, the annual sundial in this church is also a symbolic victory for the Gregorian calendar.