The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

2300-year-old Roman road connecting the empire.

Ancient snack bar of the Roman Empire re-opened.

Pompeii's less famous neighbor is still revealing her secrets.

The oldest volcanology research center in the world.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

The first green space constructed on an elevated viaduct.

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

Medieval museum built over Roman baths that features famous tapestries of a lady and a unicorn.

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

A surrealist timepiece by the artist of melting clocks.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

France's national museum of scientific and industrial instruments.

This former “ante-chamber to the guillotine” has been refurbished to illustrate the brutal history of French justice.

A museum on the history of Paris, including a set of Napoleon's toiletries, Proust's room, and relics of the Revolution.

The celebrated eyesore created by starry-eyed sweethearts.

Notorious artist squat renovated into legal studios.

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

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

A former steam-powered mill from the 1800s is now an industrial park with a giant steel dragon slide.

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

A unique underground structure dating back to the 1st century BC.

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